Do A193 Grade B8 Class 2 bolts require a class 2 nut?

ASTM A193 Grades B8 and B8M Class 2 are grades of stainless steel bolts that are strain hardened and therefore have higher yield and tensile strengths than A193 Grades B8 and B8M Class 1 bolts. However, the ASTM A193 specification does not indicate a nut requirement used with Class 2 bolts, other than simply A194 Grade 8 or 8M.

If strain hardened nuts are required, there is a supplementary requirement S1 under ASTM A194 titled “Strain-Hardened Austenitic Steel Nuts.” Strain hardened Grade 8, 8C, 8T, 8M, 8F, 8P, 8N, or 8MN may be specified. Nuts made to this supplementary requirement are higher in strength and marked with the grade symbol underlined.

The industry standard is to typically provide “regular” A194 Grade 8 or 8M nuts with Class 2 bolts. However, the ultimate determination of nut compatibility should be made the Engineer of Record.  If you are purchasing Class 2 bolts, check the project specifications to determine if strain hardened nuts are required with Class 2 bolts. If strain hardened nuts are required, A194 Supplementary Requirement S1 must be specified on the order.

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