MIL-PRF-27G
3.3.3.3 Ceramic materials (external use). Ceramic material, when used, shall be selected to enable the part to
meet the requirements of this specification. Additional information and guidance on ceramic materials is provided in
6.16.
3.3.4 Wire.
3.3.4.1 Magnet wire. Magnet wire, when used, shall be selected to enable the part to meet the requirements of
this specification. Additional information and guidance on magnet wire is provided in 6.17.
3.3.4.2 Insulated wire. Insulated wire, when used, shall be selected to enable the part to meet the requirements of
this specification. Additional information and guidance on insulated wire is provided in 6.18.
3.3.5 Solder and soldering flux. Solder and soldering flux, when used, shall be selected to enable the part to
meet the requirements of this specification. Additional information and guidance on solder and soldering flux is
provided in 6.19.
3.3.5.1 Surface Mount Device (SMD) soldering. For SMD style product, internal solder connections, minimum
reflow temperature shall be higher than the next higher assembly soldering temperature as specified on the individual
specification sheets.
3.3.6 Screws, nuts, and washers. All mounting and terminal screws, nuts, and washers shall be of
corrosion-resistant material or shall be protected against corrosion.
3.4 Interface and dimensions.
3.4.1 Mounting screws and mounting inserts. Screw threads shall be class 2A or 2B, as applicable (see 3.1), in
accordance with FED-STD-H28. External screw threads, class 2 fit, after receiving a finish, shall be capable of
accepting a nut of class 2B fit and internal screw threads; class 2 fit, after receiving a finish, shall be capable of
accepting a screw of class 2A fit with maximum installation torque in accordance with the following:
Torque
Screw size
(pound-inches)
.112-40 UNC - - - -
3
.138-32 UNC - - - -
5
.164-32 UNC - - - -
6
.190-32 UNF - - - -
8
.250-20 UNC - - - -
8
.312-18 UNC - - - -
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Nuts shall run down to within two threads of mounting surface.
3.4.2 Metals. Metal surfaces shall be corrosion resistant or shall be plated or treated to resist corrosion and shall
meet the requirements specified in 3.4.3.
3.4.3 Terminals (see 3.1).
3.4.3.1 Solder terminals (see 4.7.2.2). Solder terminals may be of any shape and shall be capable of complying
with solderability requirements of this specification (not to include insulated stranded wire or magnetic wire). The
height of the solder terminal shall be considered as the maximum distance from the terminal mounting surface to the
highest point, including the additional height obtained if semi-flexible terminals are straightened. (It is not intended that
the "hook" in the hook-type terminal be straightened from its normal hooked position.) The type of terminal and the
maximum size of wire, which the terminal will accept externally, shall be as specified (see 3.1).
3.4.3.2 Pin-type terminals for printed circuits (see 3.1). Where pin-type terminals are used the dimensions shall be
as specified (see 3.1).
3.4.3.3 Screw terminals. When specified (see 3.1, external screw terminals shall be supplied with two nuts, two
flat washers, and one lockwasher. For cased units, the height of the terminal assembly shall be the distance from the
free end of the screw to the terminal mounting surface. The type of terminal, size of screw thread, and the exposed
length of threads shall be as specified (e.g., screw, .164-32 UNC x .375) (see 3.1).
3.4.4 Mounting studs. When specified (see 3.1), external mounting studs shall be provided with a flat washer and
locknut, or with a flat washer, lockwasher, and a nut.
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