MIL-DTL-16377J(SH)
3.5 Parts and features mechanical.
3.5.1 Hardware. Unless otherwise specified in the applicable specification sheet, hardware (bolts, nuts, screws,
washers, and miscellaneous hardware) shall be of a good commercial grade material compatible with that of the
basic fixture. Steel (corrosion-resisting steel excepted) hardware shall be zinc plated.
3.5.2 Dimensions and tolerances. Dimensions shall be as shown in the applicable specification sheet. Unless
otherwise specified in the applicable specification sheet, the following tolerance shall apply:
Fractional dimensions ±1/64 inch.
a.
Decimal dimensions ±0.005 inch.
b.
Angular dimensions ±0 degree 15 minutes.
c.
Unless otherwise specified in the applicable specification sheet, a tolerance of ±1/32 inch is acceptable on fractional
dimensions that are controlled by welding, brazing, and shock mounts. This wider tolerance shall not interfere with
the interchangeability of assemblies or parts.
3.5.3 Assembly fabrication. Assembled fixtures shall have no loose parts, subassemblies, or baffles that will
rattle or detract from their quiet operation during vibration tests, or from transmitted vibration under operating
conditions of the ship. Auxiliary dampening materials shall not be used for cushioning parts or wiring to achieve
acceptable quiet operation. Rivets, pads, brackets, assemblies, and subassemblies shall be securely attached to
prevent rotation, rattling, turning, or bending. No loosening of these items shall be evident at the conclusion of the
3.5.4 Drilling, countersinking, and tapping. Drilling, countersinking, and tapping shall be done before plating
or finish is applied. Tapped holes that are used for normal replacement of parts shall be countersunk.
3.5.5 Sharp edges. Sharp edges and corners that are accessible shall be given a slight radius.
3.5.6 Castings and molded parts. Castings shall be free from cold shuts, blow holes, or any imperfections that
may affect strength. Surfaces of castings shall have burrs and fins removed. Flash shall be removed from molded
parts.
3.5.7 Surface textures. Surface textures specified in the applicable specification sheet shall be in accordance
with ASME B46.1. Surface texture symbols shall be in accordance with ASME Y14.36.
3.5.8 Threaded parts and devices.
3.5.8.1 Threads. Threads for threaded fastening devices shall be in accordance with FED-STD-H28. The
threads shall be right hand, coarse-thread series, unified thread form, Class 2A or 2B or American National thread
form, Class 2. Other thread series and classes, such as fine thread, may be used where it is necessary to ensure
functional operation of the equipment. Threads shall be checked during production run with "GO" and "NO-GO"
gauges to ensure conformance to FED-STD-H28.
3.5.8.2 Engagement of threaded parts. Threaded parts shall engage by at least four full threads in soft metals
like aluminum and aluminum alloys. A minimum of three full threads shall be used in harder materials such as brass
or steel. When a screw mates with a plastic part, a threaded metal insert shall be molded therein (pressed-in inserts
are not acceptable), except as specified in 3.5.8.4.
3.5.8.3 Thread cutting screws. Thread cutting screws (sheet metal screws and self-tapping screws that remove
material while cutting the thread) shall not be used. Thread forming screws (self-tapping screws that compress the
parent material around the engagement hole while forming the thread) are acceptable.
3.5.8.4 Threads in plastics. Threads shall not be employed in plastic parts without the use of threaded metallic
inserts, except in instances where the use of the inserts would adversely affect the electrical or mechanical
characteristics of the part. Inserts shall be secured by knurling or other method that will prevent their movement in
the plastic material.
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