MIL-DTL-5521C
3.1 MS sheets. The individual item requirements shall be as specified herein and in accordance with the
applicable MS sheet. In the event of any conflict between the requirements of this specification and the
MS sheet, the latter shall govern.
3.2 First article. When specified (see 6.2), a sample shall be subjected to first article inspection in
accordance with 4.3.
3.3 Material. The leather from which back-up washers are manufactured, shall be made from cattle
hides. The finished washers shall be unimpregnated, free from soft, spongy, harsh, or raw spots and
shall be free from defects. Unimpregnated leather is defined as leather which contains no additives other
than the normal tanning agents and greases. The greases normally used during the tanning process to
lubricate the fibers shall not be considered an impregnant. However, any material added to the leather
after the normal tanning process as defined above, for the purpose of stiffening or filling the leather, shall
be considered an impregnant.
3.3.1 Finish. The leather shall be full grain, with the flesh side smooth and free from loose flesh.
3.3.2 Compatibility with fluid. The leather back-up washers shall not adversely affect or be adversely
affected by hydraulic fluid conforming to MIL-PRF-5606.
3.4. Tannage. The leather shall be tanned with chromium salts (mineral-tanned) without the use of
vegetable tanning materials (see Table I). Processes employed shall be such as to produce satisfactory
leather which will meet all requirements specified herein without the use of impregnants as defined under
3.3. The grease content specified herein shall be attained during the normal tanning process. No
degreasing shall be employed after the normal tanning process.
3.5 Form. The leather shall be in the form of special trimmed butt bends or special backs.
3.5.1 Trim of special butt bend. The butt bend will be considered a hide with the shoulder cut off at right
angle to the belly edge at the break in the fore-shank. The belly and belly slabs will be removed leaving a
36-inch (91.4 centimeter (cm) center (18 inches (45.7 cm) either side of the back bone) (see Figure 1b).
3.5.2 Trim of the special backs. A back will be considered half a hide, cut along the back bone line with
the head, neck and any portion of the wrinkled shoulder cut off. The belly and belly slab will be removed
leaving a strip not over 18 inches (45.7 cm) wide when measured perpendicular to the back bone line
(see Figure 1a).
3.6 Physical properties. The leather shall be subjected to tests in Section 4 and conform to requirements
as follows:
a. Thickness. Leather shall be selected for thickness with a minimum of splitting or skiving
(see 4.6.2).
b. Cracking resistance. A test specimen shall not crack open when subjected to cracking resistance
test (see 4.6.3).
c. Tensile strength. The tensile strength of four test specimens shall be a minimum of 2500 pounds
per square inch (psi) (17.24 Megapascals (Mpa))with an average of not less than 3000 psi (20.68 Mpa)
before splitting (see 4.6.4).
d. Elongation. Each of four test specimens shall have a minimum elongation of 24 percent and a
maximum elongation of 36 percent before splitting (see 4.6.5).
3
For Parts Inquires call Parts Hangar, Inc (727) 493-0744
© Copyright 2015 Integrated Publishing, Inc.
A Service Disabled Veteran Owned Small Business