CN1922462A - Tape measure with extended reach - Google Patents

Abstract

The invention relates to a tape measure with an extended reach, comprising: a main housing having first and second side walls and a peripheral wall extending between the side walls; a flexible blade selectively deployable from the housing; the blade having a generally curvilinear cross-section when deployed from said main housing and a generally flat profile when retracted into the main housing; the hook has a first portion disposed generally parallel to the longitudinal axis and a second portion attached to and generally perpendicular to the longitudinal axis. The hook has a weight coefficient of not greater than about 0.60. Advantageously, the blade may be no more than about 1.10 inches wide and have a width of at least 9¹/₂Foot extension.

Description

Tape measure with extended reach

This application claims the benefit of US Provisional Application No. 60/533,093, filed December 30,2003.

technical field

The present invention relates generally to tape measures, and more particularly to a self-retracting tape measure.

Background technique

A modern tape measure (or tape scale) typically includes a coiled tape that is biased toward a retracted position by a spring. The housing generally surrounds and protects the tape and the retraction spring, and the housing includes an opening through which the distal end of the tape extends. Typically, tape measure housings consist of two housing halves that are held together by one or more screws. Additionally, one of the housing halves typically includes an inwardly projecting integral strut that provides a resting point for one end of the return spring. During assembly, the spool is placed on the strut so that the strut is connected to the retraction spring, and the other half of the housing is then attached to the first half, keeping the spool with the blade wound therebetween between them. During use, the distal end of the blade is pulled out of the housing; when the blade is released, the spring pulls the blade back into the housing, thereby returning the tape to the retracted position. The retracted blade is usually wound on a spool which itself is rotatably supported on the housing.

One characteristic of tape measures of interest to consumers is "blade stickout," which is the measured length of the blade that can protrude from the housing before it is bent (folded). The general concept in the market is that the longer the overhang, the better, because the longer the overhang, the longer the distance the ruler will span, for example, the distance between the rafters of a house during construction.

While a number of methods have been used to increase stick out, none have proven entirely satisfactory. Accordingly, there remains a need for improved tape measure designs, particularly those that provide a longer reach than standard designs.

Contents of the invention

The invention relates to a tape measure. In one embodiment there is provided a tape measure comprising: a main housing having first and second side walls and a peripheral wall extending between the side walls; selectively deployable from the housing elastic blade; when the blade is deployed from the main housing, it has a generally curved cross-section, and when the blade is retracted into the main housing, it has a generally flat profile; fixed on the ruler A hook at the first end of the blade so that the hook can move a certain distance along the longitudinal axis of the blade; In part, the hook has a weight factor of no greater than about 0.60. The hook may contain titanium, for example it may consist essentially of titanium, or alternatively the hook may contain aluminium. _The width of the blade can be no greater than about 1.10 inches, and its overhang _is at least 9 ^1/2 feet, for example, the overhang can be between 9 ^1/2 feet and about ^{10 1/2} _feet , which is very beneficial. The ability to apply a retraction bias to the blade is very beneficial. The blade may include a distal end, an inner end, and an expected hook area between the distal end and the inner end; when the blade is deployed from the main housing, the distal end is between the expected hook area and the inner end and the tape measure assembly may also include a reinforcement attached to the blade in the intended hook area, with no reinforcement at the distal and inner ends, the intended hook area included in the extension test without the reinforcement The position where the ruler is usually hooked in the center.

In another embodiment, the present invention provides a tape measure comprising: a main housing having first and second side walls and a peripheral wall extending between the side walls; The elastic blade unfolded in the housing; when the blade is unfolded from the main housing, it has a substantially curved cross-section. And when the blade is retracted into the main housing, it has a generally flat profile; the blade includes a distal end, an inner end, and an expected hooking area between the distal end and the inner end; When unfolding in the housing, the distal end is deployed before the expected hooking area and the inner end; a hook fixed on the distal end of the blade so that the hook can move a certain distance along the longitudinal axis of the blade; A first portion disposed parallel to the axis, and a second portion attached to and generally perpendicular to the longitudinal axis; a reinforcement member other than but attached to the blade in the area of intended hooking, the distal end and the inner end There is no reinforcement at the top; the expected hook area includes the location where the blade would normally be hooked in a stick-out test without reinforcement. The reinforcements may comprise metal plates. The reinforcement may comprise longitudinally arranged fiber reinforcements, advantageously the fiber reinforcements comprise a material selected from the group consisting of carbon and aramid. Advantageously, the reinforcing element can be fixed by means of adhesive in the intended hooking area of the blade and/or can be fixed on the upper side of the blade. The intended hooking area may be located between about 9 and 10.5 feet from the hook. It is very beneficial for the hook to have a weight factor of not greater than about 0.60.

In another embodiment, the present invention provides a tape measure comprising: a main housing having first and second side walls and a peripheral wall extending between the side walls; An elastic blade deployed in the housing; when the blade is deployed from the main housing, it has a generally curved cross-section. And when the blade is retracted into the main housing, it has a generally flat profile; the blade includes a longitudinal axis, a distal end, an inner end and an intended hooking area between the distal end and the inner end; when When the ruler is launched from the main housing, the distal end is deployed before the expected hooking area and the inner end; the hook is fixed on the far end of the ruler so that the hook can move a certain distance along the longitudinal axis of the ruler; the The hook has a first portion substantially parallel to the longitudinal axis, and a second portion connected to the longitudinal axis and substantially perpendicular to the longitudinal axis; the blade has a substantially equal cross-sectional thickness on the inner end and the distal end; Unequal cross-sectional thickness is expected in the hook area, which is thicker away from the longitudinal axis of the blade than near the longitudinal axis; if the entire blade has a uniform cross-sectional thickness, it is expected The hook area includes the location where the gauge is normally hooked in the outreach test. Advantageously, the intended hooking area may be located between about 8 and 10.5 feet from the hook. It is very beneficial for the hook to have a weight factor of not greater than about 0.60.

Description of drawings

Figure 1 is a side view of an embodiment of a tape measure constructed in accordance with the present invention.

Fig. 2 is a perspective view of one embodiment of a tape measure housing according to the present invention, with some components (eg, screws, clips, etc.) removed from the perspective view for clarity.

Fig. 3 shows a cross-sectional view of an embodiment of the end hook of the present invention along the longitudinal axis of the blade.

Fig. 4 is a side view of the tape measure shown in Fig. 1 when the blade is stretched out.

5A-5D are cross-sectional views of several embodiments of blades suitable for the present invention.

Figure 6 shows the jig for the scale stick out test.

Detailed ways

Figure 1 shows a tape measure, generally indicated at 10, constructed in accordance with the present invention. The tape measure 10 includes a rollable measuring blade 40 and a casing 20 connected thereto. The end hook 70 is fixed on the distal end of the blade 40 . A blade biasing member, such as a retraction spring (not shown), is operably connected to blade 40 to bias the blade in a retracted direction. A locking mechanism that includes a toggle switch 16 or similar detent component to assist in controlling the movement of the blade 40 into and out of the housing 20 . One or both sides of the housing 20 may include clips 18, if desired.

The housing 20 generally includes a main housing or shell 30 and a grip member 36 mounted on the shell 30 . As shown in Figures 1 and 2, the housing 20 preferably has an approximately square shape with rounded upper rear corners, and it may have a slightly protruding nose. The housing 20 includes a pair of opposing side walls 32, an interconnected peripheral wall 34 that helps form an interior chamber that accommodates the wound portion of the blade 40, appropriate blade biasing members and a partial locking mechanism. . As shown in the figures, the perimeter wall 34 , and thus the shell 30 , can be considered to have an upper portion 22 , a lower portion 24 , a front portion 26 and a rear portion 28 . The housing 20 includes an opening 27 generally located at the lower front corner of the housing 20 where it connects with the interior chamber. The distal end of blade 40 extends through this opening 27 . Housing 20 is preferably sized to fit in the user's hand, and can also be conveniently stored in a work belt or tool box.

As shown in FIG. 2, the housing 30 may be constructed in two parts: a right hand side part 30a and a left hand side part 30b, which are joined together using suitable screws 38 as is known in the art. The outer configuration of the housing parts 30a, 30b and the grip member part 36 may advantageously be symmetrical if desired, but this is not required. In fact, the two aforementioned parts 30a, 30b may have different internal and external structures, depending on the inner workings of the tape measure 10, as is known in the art. However, since the invention is primarily concerned with blade 40 and hook 70, the details of the external construction of housing 30 are not important to an understanding of the invention. Information regarding possible external configurations of housing 20 can be found in US Patent Application Publication No. 2003/0,233,762, the contents of which are incorporated herein by reference. Note also US Patent Nos. 4,527,334, 4,976,048, 6,349,482 and 6,718,649, the contents of all of which are incorporated herein by reference for further discussion of the general structural design and operation of the self-retracting tape measure 10.

Blade 40 is designed to be selectively deployed from housing 20 and locked against retraction force by locking member 16 . The blade 40 is generally made of steel; when deployed from the housing 20 , the blade has a generally curved cross-section; and when retracted into the housing 20 , it has a generally flat profile. The upper side 42 of the ruler is usually printed or otherwise marked with length, but the lower side 44 is usually unmarked. Typically blade 40 is also typically coated with a protective coating such as that discussed in U.S. Patent Application No. 10/268,432, entitled "Coated Tape Measure Blade," referred to herein as The manner of citation includes the content of the above-mentioned application. Blade 40 may be considered to have a distal end 52 disposed along longitudinal axis 46 , an intended hooking area 54 , and an inner end 56 . When blade 40 is deployed from housing 20 , distal end 52 (and hook 70 secured thereto) protrude first, followed by intended hooking area 54 , and then inner end 56 . Blade 40 generally has an equal cross-sectional thickness T _u at least on distal end 52 and inner end 56 . If applicable, the entire blade has a uniform cross-sectional thickness, however, the blade may have different thicknesses within the intended hook area 54 . Anticipated hook area 54 includes location B, which corresponds to expected hook points when the blade is subjected to a stickout test, on the assumption that the entire blade is of uniform cross-sectional thickness. The location of point B can be deduced from theory or experience. The intended hitch point B is at a distance L from the distal end of blade 40, and the length of L is advantageously between 8 and 10.5 feet.

Blade 40 may have a uniform thickness T _u in its cross-section and along its entire length, and the entire cross-section of the blade may consist of the same material composition. As shown in FIG. 5A , as an alternative, blade 40 may have different thicknesses across its entire cross-section (at least at the intended hook-up area), and/or blade 40 may have different thicknesses along its length, and/or be formed by Composition of different material compositions. For example, the blade 40 may have a smaller thickness at its distal end 52 and a greater and uniform thickness T _R in the longitudinal region where hooking is intended. In other embodiments, blade 40 may have longitudinal integral reinforcement members 60 distributed across its cross-section. For example, the outer thickness of the blade cross-section in the width direction may be T _R , which is greater than the thickness _Tu of the middle portion of the blade side cross-section (see FIG. 5B ). Alternatively, the widthwise exterior of the blade's cross-section may have built-in longitudinal stiffeners 60, such as carbon or aramid fibers 64 arranged longitudinally or similar (see Figure 5C). Additionally, the longitudinal stiffeners 60 may take the form of a carbon or aramid fiber mesh material embedded within the primary blade material. It should be pointed out that the above-mentioned changes in the geometric shape and composition of the ruler are used to increase the hooking resistance of the ruler, so as to increase the extension of the ruler. At least the intended hook area 54 of the blade 40 should have such a reinforcing member, however, the reinforcing member can optionally be extended from the intended hook area 54 through the inner end 56 of the blade 40 (for example, the blade is connected to the back location on the retraction spring). In other embodiments, a thicker coating is provided in the expected hooking area 54 of the blade 40, and/or a reinforcement on the blade 40 is fixed (such as riveted, bonded, or otherwise fixed). plate 62 (see Figure 5D). Although the reinforcing plate 62 is shown adjacent to the upper side 42 in FIG. 5D, as an alternative, the reinforcing plate may be adjacent to the lower side 44, or a reinforcing plate may be provided on each side 42, 44 of the blade 40 if desired. 62.

The end hook 70 is fixed on the distal portion 52 of the blade 40 . The end hooks 70 generally serve a dual purpose: providing hooking or securing of the blade 40 to a remote point and preventing the blade 40 from being retracted into the housing. The hook 70 includes a first portion 72 disposed generally parallel to the longitudinal axis 46 of the blade 40 and a second portion 76 with a suitable curved joint 78 therebetween. Portion 76 is disposed generally perpendicular to longitudinal axis 46 of blade 40 . The first portion 72 is sometimes referred to in the art as the knuckle portion and the second portion 76 is referred to as the tip portion. Advantageously, the hook first portion 72 may have a curved shape corresponding to the concave curve of the cross-section of the blade when the blade is unfolded. Beneficially, the first portion 72 may also include one or more (for example four) holes 74 for fixing the hook 70 to the upper side 42 of the blade 40 by means of suitable connecting means, such as rivets or the like. superior. The size of the above-mentioned holes 74 can be slightly larger than the size of the corresponding connecting parts, so that the hook 70 can be moved relative to the blade 40 by an amount of X, so that the amount of movement X can be the thickness of the second part 76 of the hook. , allowing the tape measure to be used for external or internal measurements. Additionally, as described in US Patent No. 5,659,970, the holes 74 may be positioned so that the retraction stop load is properly distributed. The contents of the aforementioned US patent applications are incorporated herein by reference. The hook second portion 76 may include a suitable central hole (not shown), which is generally oval in shape, to accommodate the exposed head of the nail so that the tape measure 10 can be rotated about the nail. Additionally, if desired, the second portion 76 may include one or more magnets (not shown) to magnetically secure the hook 70 to a surface measurement or test point.

For reasons of required strength and durability, in the prior art steel is used for the hook of the tape measure. For example, a good-quality tape measure needs to have hooks that can withstand repeated retraction movements of the blade (eg, the number of retractions ≥ 2,000 times). Although low carbon steel (i.e., Type 1050) is suitable for this application, steel is a relatively heavy material, and the inventors of the present invention have found that the added weight of the steel end hooks at the end of the tape measure creates an impact on the extension of the blade 40. Negative Effects. In particular, if the weight of the hook 70 is reduced, the protrusion of the blade can be increased. However, merely reducing the size of the hook 70 can adversely affect the strength, durability, and utility of the hook 70, especially after the blade 40 has been retracted many times. Accordingly, preferred embodiments of the present invention utilize hooks 70 having a weight factor of no more than about 0.60, as the term "weight factor" is used herein refers to the weight ratio of a hook 70 to a steel hook of the same size. For example, to maintain the required durability, some embodiments of the present invention having blades 40 about 1 inch wide have hooks 70 made of titanium or a titanium alloy having a weight of 2.27 grams force, Whereas a steel hook of the same size has a weight of 4.08 grams force, resulting in a weight factor of 0.556. This reduces the weight of the hook 70 at one end of the blade 40 by nearly half while maintaining the desired size and durability. Examples of alternative materials for hook 70 include aluminum and aluminum alloys that are stamped or cast.

The tape measure 10 of the present invention is constructed to provide improved reach. One method of measuring the extension is: stretch the blade 40 from the housing 20 until the blade hangs down under its own gravity (the present invention generally refers to this as "bending" or "bending") . Using a standard jig makes it easy to compare the construction of different tape measures. Figure 6 shows an example of a clamp 90 that may be used. Clamp 90 includes a 4 inch high support bracket 92 with _an upper edge having a radius of ^1/2 inch. Support bracket 92 may include two pivot pins 94 (eg, 1/8 inch pivot pins) or other components that prevent blade 40 from sliding sideways. A 1 inch diameter horizontal pin 96 is set back 6 inches from the center of the bracket 92 to leave a 7/32 inch gap between the horizontal pin 96 and the bottom flange 98 . The tape measure 10 is placed behind the horizontal pin 96 and the blade 40 is paid out from above the support bracket 92 . The blade 40 is stretched slowly until it bends. In the presence of the hook 70, the distance from the centerline of the support bracket 92 to the hook 70 (more precisely, the distal surface of the second portion 76) is the value of the degree of extension. In most embodiments, the tape measure 10 according to the present invention has a stickout of at least ⁹ _1/2 feet with blades 40 having a width of about 1 inch.

Experiments were conducted to show that the reach can be increased by using hooks 70 having a weight factor of 0.60 or less. Two existing products with steel end hooks were measured using the test procedure outlined above. In the test, the rivets securing the steel hook 70 to the blade 40 were removed to loosen the steel hook. Then steel hooks and rivets were fixed on one end of the ruler 40 with scotch tape, and the overhang of each sample with the above-mentioned structure was measured three times using the above-mentioned clamp 90 . The steel hook 70 is removed, and a titanium hook 70 of the same form factor is then secured to one end of the same blade 40 (along with the rivets) by scotch tape. The stick out of each sample was then measured three times using the jig 90 described above. Steel hooks weigh 0.0084 lbs and titanium hooks 70 weigh 0.0046 lbs. Thus, all other variables being equal, the tests comparing stick out results using hooks of different weight factors are shown in Table 1 below.

Table 1 - Stick Out Results (Inches) Lufkin ^(R) 2125 tape measure Luflkin ^(R) PS3425 Tape Measure sample steel hook titanium hook sample steel hook titanium hook 1A 82.0 84.0 6A 82.5 87.5 1B 81.5 84.0 6B 82.0 86.5 1C 81.5 84.5 6C 82.5 87.0 2A 76.0 82.0 7A 85.0 87.5 2B 76.0 82.0 7B 84.5 87.5 2C 76.0 82.0 7C 87.0 87.0 3A 75.5 80.5 8A 85.0 85.0 3B 75.0 81.0 8B 85.0 87.0 3C 75.5 81.0 8C 85.0 86.5 4A 82.0 83.5 9A 84.5 87.0 4B 82.0 85.0 9B 84.5 86.0 4C 82.0 83.0 9C 84.5 86.5 5A 83.0 84.0 10A 82.5 85.5 5B 82.0 85.0 10B 82.5 87.0 5C 83.0 85.0 10C 82.5 87.0 average value 79.5 83.1 average value 83.8 86.7

These test results show that the use of hooks with a weight factor of less than 0.60 increases stick out. For the Lufkin ^(R) 2125 blades, the stick out increased by an average of about 3.6 inches. For the Lufkin ^(R) PS3425 blades, the stick out increased by an average of about 2.9 inches.

We performed another set of experiments using a Max Steel(R ^{) tape} measure, available from Stanley Works of New Britain, Connecticut. This tape measure uses a 1-inch wide blade that measures up to 25 feet in length. This set of tests was conducted in a manner similar to that given above, with steel hooks weighing 0.0086 lbs and titanium hooks 70 weighing 0.0051 lbs. Thus, all other variables being equal, the test compared the stick out results using hooks of different weight factors. The test results are shown in Table 2.

Table 2 - Stick Out Results (Inches) Max Steel ^® tape measure sample steel hook titanium hook 1A 90.0 102.0 1B 90.5 104.0 1C 90.5 104.5 2A 99.0 103.0 2B 99.0 103.0 2C 99.0 104.0 average value 94.7 103.4

These test results show that the use of hooks with a weight factor of less than 0.60 increases stick out. For the Max Steel ^(R) blades, the stick out increased by an average of about 8.7 inches.

While the test results given above have a stickout of less than 9 ^1/2 _inches , one skilled in the art should be able to adjust the thickness of the blade, the shape of the blade, and/or other characteristics to increase the stickout to Ideal length. For additional information in this regard, attention is drawn to US Patent No. 6,324,769, the content of which is incorporated herein by reference.

It should be understood that the tape measure 10 of the present invention may also include other features, for example it may include a shock absorbing bumper adjacent the opening 27, specially coated blades, various locking mechanisms, hook reinforcement plates and the like. These are all known in the art.

The present invention may, of course, be carried out in other ways than those set forth herein without departing from essential characteristics of the invention. Therefore, the present embodiments should be considered in all respects as illustrative and not restrictive. All changes within the meaning and range of equivalents of the following claims are included in this range.

Claims (23)

1. A measuring tape comprising: a main housing having first and second side walls and a peripheral wall extending between the side walls; a resilient blade selectively deployable from the housing; when the blade is deployed from the main housing, it has a generally curvilinear cross-section and when the blade is retracted When inside the main housing, it has a generally flat profile; a hook fixed to the first end of the blade so that the hook can move a distance along the longitudinal axis of the blade; the hook has a first portion substantially parallel to the longitudinal axis, and is connected to the A second portion on and substantially perpendicular to the longitudinal axis, the hook having a weight factor of not greater than about 0.60. 2. The tape measure of claim 1, wherein the hook comprises titanium. 3. The tape measure of claim 2, wherein said hook consists essentially of titanium. 4. The tape measure of claim 1, wherein the hook comprises aluminum. 5. The tape measure of claim 1, wherein said blade has a width of no greater than about 1.10 inches and has an overhang of at least 9  feet. 6. The tape measure of claim 5, wherein the tape measure has a stick out of between 9 Fft and about 10 Fft. 7. The tape measure of claim 1, wherein a retraction bias is applied to the blade; said hooks contain titanium; The blade has a width of no greater than about 1.10 inches and has an overhang of at least 9 inches. 8. The tape measure of claim 1, wherein The blade includes a distal end, an inner end, and an intended hooking area between the distal end and the inner end; when the blade is deployed from the main housing, the distal end is said intended hooking area and said inner end are forwardly deployed; the tape measure also includes a reinforcement attached to said blade in said intended hooking area, said distal end and said inner end being free of reinforcement; and Wherein, the expected hook area includes the position where the blade is usually hooked in the extension test without the stiffener. 9. The tape measure of claim 8, wherein the hook comprises titanium. 10. The tape measure of claim 8, wherein the blade has a width of no greater than about 1.10 inches and has an overhang of at least 9  feet. 11. A tape measure comprising: a main housing having first and second side walls and a peripheral wall extending between the side walls; a resilient blade selectively deployable from the housing; when the blade is deployed from the main housing, it has a generally curvilinear cross-section and when the blade is retracted When inside the main housing, it has a generally flat profile; the blade includes a distal end, an inner end, and an intended hooking area between the distal end and the inner end; when the blade is removed from When deployed within the main housing, the distal portion deploys ahead of the intended hooking area and the inner end; a hook fixed to the distal end of the blade so that the hook can move a distance along the longitudinal axis of the blade; the hook has a first portion substantially parallel to the longitudinal axis, and is attached to the a second portion on and generally perpendicular to the longitudinal axis; said distal end portion and said inner end portion are free of said reinforcement members other than said blade but connected to said blade in said intended hooking area; The expected snag area includes a location where the blade would normally snag in a stickout test without the stiffener. 12. The tape measure of claim 11, wherein the stiffener comprises a metal plate. 13. The tape measure of claim 11, wherein the reinforcement comprises a longitudinally disposed fiber reinforcement. 14. The tape measure of claim 13, wherein the fiber reinforcement comprises a material selected from the group consisting of carbon and aramid. 15. The tape measure of claim 11, wherein said stiffener is secured by adhesive in said intended hook area of said blade. 16. The tape measure of claim 11, wherein the intended hook area is located between about 9 and 10.5 feet from the hook. 17. The tape measure of claim 11, wherein the hook has a weight factor of not greater than about 0.60. 18. The tape measure of claim 11, wherein said stiffener is secured to an upper side of said blade. 19. The tape measure of claim 11, wherein said intended hooking area is located between about 9 and 10.5 feet from said hook; the hook has a weight factor of not greater than about 0.60; and The reinforcement includes a metal plate. 20. The tape measure of claim 11, wherein said intended hooking area is located between about 9 and 10 feet from said hook; said reinforcement includes a longitudinally disposed fiber reinforcement comprising a material selected from the group consisting of carbon and aramid; and The hook has a weight factor of not greater than about 0.60. 21. A tape measure comprising: a main housing having first and second side walls and a peripheral wall extending between the side walls; a resilient blade selectively deployable from the housing; when the blade is deployed from the main housing, it has a generally curvilinear cross-section and when the blade is retracted When it is inside the main housing, it has a generally flat profile; the blade includes a longitudinal axis, a distal end, an inner end, and an intended hooking area between the distal end and the inner end; When the blade is deployed from the housing, the distal end is deployed before the expected hooking area and the inner end; a hook fixed to the distal end of the blade so that the hook can move a distance along the longitudinal axis of the blade; the hook has a first portion substantially parallel to the longitudinal axis, and is attached to the a second portion on and generally perpendicular to the longitudinal axis; said blade has a substantially equal cross-sectional thickness at said inner end and said distal end; said blade has a non-uniform cross-sectional thickness across said intended hooking area, the blade being thicker away from said blade longitudinal axis than adjacent said longitudinal axis; If the entire blade has a uniform cross-sectional thickness, the expected hook area includes the location where the blade would normally be hooked in a stickout test. 22. The tape measure of claim 21, wherein the intended hook area is located between about 8 and 10.5 feet from the hook. 23. The tape measure of claim 21, wherein the hook has a weight factor of not greater than about 0.60.

Images