FF-S-85D
3.3.2 Thread series, class, lengths, and hand. Unless otherwise specified (see
6.2), cap screws shall be right - hand of the UNC (coarse thread) or UNF (fine
thread) series, Class 2A, in accordance with FED-STD-H28/2.
3.3.3 Threads protectively coated. Unless otherwise specified (see 6.2),
threads protectively coated shall meet the dimensions of FED-STD-H28/2 after the
coating has been applied.
3.3.4 Bearing surface. Bearing surface of cap screw heads, except flat head,
shall be at right angles to the axis of the body within a tolerance of 2 degrees
and of hex head within a tolerance of 2 degrees for 1 inch size and smaller, and 1
degree for sizes larger than 1 inch. The axis of the head shall be concentric
with the axis of the body (determined by one diameter length of body under head)
within a tolerance equal to 3 percent (6 percent TIR) of maximum width across
flats. Any mutilation of the bearing surface sufficient to prevent proper seating
of the screw shall be cause for rejection.
Protective coatings.
3.4
3.4.1 Coatings. Cap screws shall be furnished uncoated, passivated, or coated
as specified herein (see 6.2).
3.4.2 Passivation. Corrosion resistant steel cap screws shall be passivated in
accordance with SAE-AMS-QQ-P-35.
3.4.3 Cadmium plating. When specified (see 6.2), cap screws shall be cadmium
plated in accordance with SAE-AMS-QQ-P-416, Type II, Class 2.
3.4.4 Zinc plating. When specified (see 6.2), cap screws shall be zinc plated
as specified in ASTM B633, type II, class FE/ZN 5.
3.4.5 Anodizing. Unless otherwise specified, aluminum alloy cap screws shall
be electrolytically treated in conformance to MIL-A-8625, type II, class 1, non-
dyed (see 6.2).
3.4.6 Phosphate. When specified (see 6.2), cap screws shall be treated in
conformance to MIL-DTL-16232, type Z, class 2.
3.4.7 Black chemical. When specified (see 6.2), brass cap screws shall be
treated with a black chemical finish in accordance with MIL-F-495.
3.4.8 Hydrogen embrittlement. Alloy steel cap screws required to be
electroplated or phosphate coated (see 3.4.3 thru 3.4.6) shall be subjected to a
relief treatment in accordance with the methods specified in the applicable
plating or coating specification, immediately after the plating or coating
operation to minimize the embrittlement that results from these processes.
Metallographic requirements.
3.5
3.5.1 Decarburization. When specified (see 6.2), the partial decarburization
of threads of steel cap screws, then tested in accordance with 4.4.4.1, shall not
exceed the amount shown in figure 1.
3.5.2 Grain size of copper alloy. When specified (see 6.2), grain size of
copper alloy in cap screws shall be an option of the contracting officer in
accordance with the material specification.
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