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Thread Pitch of SA-194 Nuts

Thread Pitch of SA-194 Nuts

Thread Pitch of SA-194 Nuts

Hi All,

I have a few questions regarding metric nuts according to SA-194/SA194M. For reference, I am working in the 2007 Edition of the Code (2009a Addenda).

Paragraph 8.2 states: "Unless otherwise specified, threads shall be in accordance with ANSI B 1.1 or ANSI B 1.13M, and shall be gaged in accordance with ANSI B 1.2 and ANSI B1.13M as described in 8.2.1 and 8.2.2."

Paragraph 8.2.1 states: "8.2.1 Nuts up to and including 1 in. nominal size shall be UNC Series Class 2B fit. Metric nuts up to and including M24 nominal size shall be coarse thread series tolerance 6H."

A client wants to use M20x1.5 nuts. The 1.5 pitch is listed in B1.13M. However, 1.5 mm pitch falls under the fine series. My interpretation of paragraph 8.2 and 8.2.1 is that coarse series thread must be used, i.e. 2.5 mm pitch to comply with SA-194. Am I interpreting this correctly or am I being overly strict? Is it possible to read the "Unless otherwise specified" clause in paragraph 8.2 to apply to the pitch meaning a 1.5 mm pitch is allowed.

If am being too strict, how should I interpret paragraph 7.2.1 which states: "All nuts shall be capable of withstanding the proof loads specified in Table 3 and Table 4. However, nuts manufactured to dimensions and configurations other than those covered by ANSI B 1.1, ANSI B 1.13M, ANSI B 18.2.2, and B are not subject to the proof load test." The nuts are manufactured to B1.13M and therefore must be capable of withstanding the proof loads as specified in Table 4.

Table 4 gives the proof load for M20x2.5 nuts (not 1.5). Should the same proof load then be used for 1.5 mm pitch nuts as for 2.5 mm pitch nuts?

Thank you in advance.

RE: Thread Pitch of SA-194 Nuts

in 2019 edition also it is mentioned that M20 nut shall have coarse pitch.
It is better to use coarse pitch as mentioned in code so that there will not be doubts pertaining to proof load.

You can check with your client if they are ok with coarse pitch. You can share with them the doubts pertaining to proof load.

Do give us the feedback about client's decision.

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