---
kind: "section"
citation: "30 C.F.R. § 7.305"
title: "30"
number: "7.305"
heading: "Critical characteristics."
url: "https://uscodex.org/cfr/30/7.305"
---

# §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](/cfr/30/7.304.md) of this part.

## Notes

### Source

Source: 57 FR 61193, Dec. 23, 1992, unless otherwise noted.

### Authority

Authority: 30 U.S.C. 957.

### Source

Source: 53 FR 23500, June 22, 1988, unless otherwise noted.