MIL-DTL-45916C
4.5.3 Concentricity. The internal thread pitch diameter shall be examined for concentricity
with the external thread pitch diameter using a comparator and suitable thread form chart.
Concentricity shall be checked while rotating the insert and observing the total eccentricity of the
external thread pitch diameter relative to the thread chart.
4.6 Tests.
4.6.1 Installation. Each insert taken as specified in 4.3.2 shall be visually inspected under
10X magnification and installed in accordance with MS35914 or MS51837 in test blocks
specified in 4.4.1. The presence of cracks in either the test block or the insert as a result of
installation shall be cause for rejection. When visual inspection discloses a condition which shows
cause for further examination, the test specimen shall be magnetic particle or penetrant inspected
in accordance with ASTM E1444/E1444M or ASTM E1417/E1417M.
4.6.2 Internal thread self-locking. Test specimens installed into test blocks (Figure 3) as
specified in 4.6.1 shall be used for torque testing of the internal thread locking feature, when
applicable. Specimens used for the pullout and rotational resistance tests shall not be used for the
self-locking test.
4.6.2.1 Screw-locking torque. The torque test shall consist of a 15 cycle room temperature
torque test, using test bolts or screws in accordance with 4.4.2 having sufficient thread length to
extend beyond the locking feature a minimum of two pitches (including bolt thread chamfer). A
new bolt or screw and a new test specimen shall be used for each complete 15 cycle test. Bolts
and screws shall assemble freely, with the fingers, up to the locking feature. The bolt or screw
shall be engaged and disengaged from the insert self-locking area for 15 full installation and
removal cycles with no axial load on the insert. The test shall be run at a rate slow enough to yield
a dependable measure of torque and avoid heating of the bolt. A bolt shall be considered fully
installed when two threads extend past the end of the locking feature of the insert; the removal
cycle shall be considered complete when the locking feature is disengaged.
4.6.2.2 Maximum locking torque. Maximum locking torque shall be the maximum torque value
encountered on any installation or removal cycle, and shall not exceed values specified in Table I.
Maximum locking torque readings shall be recorded on the first, seventh and fifteenth installation
cycle.
4.6.2.3 Minimum breakaway torque. Minimum breakaway torque shall be the minimum torque
required to start removal of the screw or bolt from a fixed position during the first one-half turn of
the removal cycle. The torque value for any cycle shall not be less than the applicable value
specified in Table I. Minimum breakaway torque reading shall be recorded at the start of the first,
seventh and fifteenth removal cycle.
4.6.3 Pullout resistance. Test specimens installed into test blocks (Figure 2), as specified in
4.6.1 shall be used for the pullout resistance test. The test bolt shall assemble freely into the
insert, prior to engaging the self-locking device, with finger torque and shall be of sufficient length
to extend through the insert a minimum of two pitches (including bolt thread chamfer). The
bushing and test block clearance holes in the upper and lower yokes (Figure 4) shall have a free
fit not in excess of 0.060 inch greater than the bushing and test block diameters. The bolt
clearance hole in the upper bushing (Figure 4) shall be 0.005 to 0.015 inch diameter larger than
the nominal diameter of the test bolt. The minimum pullout strength specified in Table II shall then
be applied to the assembly. Failure of the insert to stay in the test block or failure of the internal
thread shall not occur below the loads specified in Table II. If bolt failure occurs below the
applicable pullout strength rating, the test shall be repeated until the minimum pullout strength of
the insert is exceeded. Rate of loading shall not exceed 100,000 PSI per minute per square inch
based on the shank diameter area of the bolt.
4.6.4 Rotational resistance. Test specimens installed into test blocks (Figure 3), as specified
in 4.6.1 shall be used for the rotational resistance test. When the near side face of the insert is
installed in accordance with MS35914 or MS51837, the far side of the insert shall extend a
distance of one and one-half to two external thread pitches of the insert past the far side of the
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