Critical characteristics.

§ 7.305 Critical characteristics. 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 flame-arresting path. (b) Clearances between mating parts that form flame-arresting paths. (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.