30 CFR § 7.305
The following critical characteristics shall be inspected on each motor
assembly to which an approval marking is affixed:
(a) Finish, width, and planarity of surfaces that form any part of a
(b) Clearances between mating parts that form flame-arresting
(c) Thickness of walls, flanges, and covers that are essential in
maintaining the explosion-proof integrity of the enclosure.
(d) Spacing of fastenings.
(e) Length of thread engagement on fastenings and threaded parts
that assure the explosion-proof integrity of the enclosure.
(f) Use of lockwasher or equivalent with all fastenings.
(g) Dimensions which affect compliance with the requirements for packing
gland parts in §7.304 of this part.