Why is the nut stronger than the bolt?

If a joint is overloaded, the bolt should stretch visibly rather than the nut thread stripping without warning. The standards are set up so the bolt fails first.

Can I use a 2H nut on a B8M stud?

No. Use a stainless 8M nut on B8M, so both parts have the same corrosion resistance and no galvanic pair forms.

Heavy hex or regular hex for flanges?

Heavy hex. ASME B16.5 flange bolting uses heavy hex nuts to ASME B18.2.2 (inch) or ASME B18.2.4.6M (metric).

Do the nuts need an impact test for cold service?

Yes, with L7 studs specify impact-tested grade 7 nuts. They are marked with an L.

Can I order studs and nuts as one set?

Yes – our stud bolt configurator adds the matching nuts automatically, with certificates for both.

What about 8.8 bolts with class 10 nuts?

That works: a stronger nut is always allowed. The other way round is not.

Technical guide

Which nut goes with which bolt?

Match the nut to the bolt grade: B7 with 2H, B7M with 2HM, B16 and L7 with grade 7, B8 with 8 and B8M with 8M. In metric property classes, a class 8 nut goes with an 8.8 bolt, 10 with 10.9, 12 with 12.9 – and A2-70 or A4-80 nuts with the same stainless class.

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Short answer

The nut is designed to be stronger than the bolt, so the bolt yields first – never the thread in the nut.
Match "M" grades with "M" nuts: B7M + 2HM.
Match stainless with the same stainless: B8M + 8M, A4-80 + A4-80.
Flange bolting uses heavy hex nuts to ASME B18.2.2 (inch) or ASME B18.2.4.6M (metric).

ASTM bolting

Stud and nut pairs for flanges.

Stud / bolt	Nut (ASTM A194)	Why
A193 B7	2H	Default pair for high-pressure flanges
A193 B7M	2HM	Both hardness-limited for sour service
A193 B16	7	Cr-Mo nut for elevated temperature
A320 L7	7, impact-tested (marked L)	Toughness at low temperature for nut and stud alike
A320 L7M	7M, impact-tested	Low temperature plus hardness limit
A193 B8 (304)	8	Same stainless grade
A193 B8M (316)	8M	Same stainless grade, molybdenum for chlorides

ISO property classes

Metric bolts and nuts.

Bolt	Nut	Standard
8.8	8	ISO 898-1 / ISO 898-2
10.9	10	ISO 898-1 / ISO 898-2
12.9	12	ISO 898-1 / ISO 898-2
A2-70	A2-70	ISO 3506-1 / ISO 3506-2
A4-70	A4-70	ISO 3506-1 / ISO 3506-2
A4-80	A4-80	ISO 3506-1 / ISO 3506-2

Watch out for

Three common mistakes.

01Galling on stainlessStainless bolt and nut of the same grade can seize when tightened. Use an anti-seize lubricant, or a PTFE / Xylan coating.
02Hot-dip galvanized studsThe zinc layer is thick, so the nuts must be tapped oversize (ISO 10684). A standard nut will not fit – order the set together.
03Mixing certificatesStud and nut each need their own certificate and heat number. Ordering them as one set from us keeps the paperwork together.

FAQ

Questions we get every week.

Why is the nut stronger than the bolt?: If a joint is overloaded, the bolt should stretch visibly rather than the nut thread stripping without warning. The standards are set up so the bolt fails first.
Can I use a 2H nut on a B8M stud?: No. Use a stainless 8M nut on B8M, so both parts have the same corrosion resistance and no galvanic pair forms.
Heavy hex or regular hex for flanges?: Heavy hex. ASME B16.5 flange bolting uses heavy hex nuts to ASME B18.2.2 (inch) or ASME B18.2.4.6M (metric).
Do the nuts need an impact test for cold service?: Yes, with L7 studs specify impact-tested grade 7 nuts. They are marked with an L.
Can I order studs and nuts as one set?: Yes – our stud bolt configurator adds the matching nuts automatically, with certificates for both.
What about 8.8 bolts with class 10 nuts?: That works: a stronger nut is always allowed. The other way round is not.

Next step

Configure, download or ask.

Reviewed October 2026 by HBS Solutions. Based on ASTM A193, A320 and A194, ISO 898-1/-2 and ISO 3506-1/-2. Values are minimums from the standard; always check the edition and options named in your project specification.

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