MIL-DTL-24749B(SH)
3.2.2.1 Bimetallic boss. The foot of the aluminum boss shall be manufactured from aluminum alloy 5083,
5086, or 5456, in accordance with ASTM B928/B928M. The foot shall be bonded to CRES 316, UNS S31600 to
form the Aluminum/CRES boss. An interstitial layer of an appropriate metal may be used to enhance strength and
weldability. Acceptable interstitial metals include chromium, tantalum, molybdenum, and titanium.
3.2.2.2 Bolts. Bolts used in conjunction with bosses shall be fabricated from CRES 316, UNS S31600. The
bolt for attachment of the Type I bond strap to the boss shall be 3/8-16 x ¾ inches in accordance with ASTM F593 or
MIL-DTL-1222 (see 6.2).
3.2.3 Type II bond strap. Type II bond straps shall be manufactured of annealed CRES 316, UNS S31600 in
accordance with ASTM A240/A240M or ASTM A666. Thickness of strap shall be 0.024±0.003 inch.
3.2.4 Type III bond strap. Type III bond straps shall be manufactured of UNS C11000 (Electrolytic Tough
Pitch) Temper H00 (cold-rolled) flat copper strip, in accordance with ASTM B152/B152M. Thickness of strap shall
be 0.024±0.003 inch.
3.2.5 Type IV bond strap. Type IV bond straps shall consist of three components:
a.
One wire braid strap
b.
Two end terminals
Ensure that both mounting surfaces of the terminals are smooth and flat; and burnish the end to remove sharp
edges.
3.2.5.1 Braid. Bond strap braid shall be 50 percent CRES 316 wires and 50 percent Nickel 200 wires of 36
American Wire Gauge (AWG). The braid shall be constructed in accordance with A-A-59569, PIN number
36*1000, using 6 strands of 36AWG Nickel 200 wire and 6 strands of 36AWG CRES 316L stainless steel, woven
on a 64 carrier machine with 768 ends to produce an approximately 1-inch wide flat braid strap.
3.2.5.2 End terminal. End terminals shall be annealed, wall welded, or seamless, CRES 316L tube in
accordance with ASTM A269. Dimensions shall be 1.18±0.02 inch in length with an O.D. of 0.625 inch and
nominal wall thickness of 0.065 inch. The end of the braid shall lay 100 percent inside the tube and the tube shall
be flattened to 0.15±0.010 inch onto the braid. Drill or punch 13/32 inch (0.406) ±0.001-inch hole in each lug to
facilitate 3/8-inch bolts (for Size Code A-C), or 9/32 inch (0.282) ±0.001 inch-hole in each lug to facilitate ¼-inch bolts
(for Size Code D-F).
3.3 Construction. Bond strap and boss dimensions shall conform to tables I through IV and the following:
3.3.2.1 Boss bolts. Boss bolts shall conform to paragraph 3.2.2.
3.3.3 Type II. Type II bond straps shall conform to paragraph 3.2.3 and figure 3. The length-to-width ratio
shall not exceed 5 to 1.
3.3.4 Type III. Type III bond straps shall conform to paragraph 3.2.4 and figure 3. The length-to-width ratio
shall not exceed 5 to 1.
3.3.6 Dimensions. Bond strap dimensions shall be as specified herein. Dimensions are in inches. Unless
otherwise specified (see 6.2), strap length shall be of standard sizes as detailed in section 1.2.1.
3.4 Performance requirements.
3.4.1 Visual inspection. When tested as specified in 4.5.1, bond straps shall meet the requirements in 3.2, 3.3,
3.4.2 Bond joint strength and uniformity. The bimetallic boss joint shall be tested as specified in MIL-J-24445
and shall meet the requirements for both gas and electric arc weld studs in MIL-J-24445.
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