The short answer: The common A193/A194 pairings are B7 with 2H, B7M with 2HM, B8 with Grade 8, and B8M with Grade 8M. B8C commonly pairs with 8C and B8T with 8T. These are starting pairings, not permission to ignore diameter, thread, proof load, finish, temperature or the governing joint design.[1] [2] [3]
For the full material series, start with the A193 and A194 guide. Read the ASTM A194 nuts guide when you need the nut specification itself. This page answers one narrower question: which A194 nut should be ordered with an A193 stud or bolt?
A193 bolt to A194 nut pairing chart
| ASTM A193 bolting | Material route | Common ASTM A194 heavy hex nut | Detailed pages |
|---|---|---|---|
| B7 | Quenched-and-tempered Cr-Mo alloy steel | 2H | B7 bolting |
| B7M | Controlled-hardness Cr-Mo alloy steel | 2HM | B7M bolting |
| B8 Class 1, Class 2 or Class 2B | Type 304 stainless steel | 8 | B8 bolting |
| B8M Class 1 or Class 2 | Type 316 stainless steel | 8M | B8M bolting |
| B8C | Type 347 stabilized stainless steel | 8C | B8C requirements remain a separate callout |
| B8T | Type 321 stabilized stainless steel | 8T | B8T requirements remain a separate callout |
The pairings align material families and common mechanical requirements. They do not make the bolt and nut one specification: the purchase order must state both ASTM designations and both grades.
Why the nut cannot be selected by diameter alone
A nut must carry the intended bolt load without thread stripping or prohibited deformation. That depends on nut material, proof load, hardness, thread stress area, engagement, style and dimensions. Two nuts that fit the same thread can have different proof-load requirements and different service limitations.[2] [3]
| Check | Why it matters |
|---|---|
| A193 grade and class | Establishes bolt material and mechanical condition |
| A194 grade | Establishes nut material and property route |
| Nominal size and pitch | Controls thread compatibility and stress area |
| Heavy hex or other style | Changes dimensions and tabulated proof load |
| Finish | Affects thread allowance, friction and corrosion behavior |
| Design temperature/environment | Controls final material and coating suitability |
B7 with A194 2H
ASTM A193 B7 commonly uses ASTM A194 Grade 2H. This is the standard high-strength alloy-steel bolting route for many flange and pressure-joint applications. State the 2H nut separately, including heavy hex dimensions, thread and finish.
Do not replace 2H with a stainless nut simply to gain corrosion resistance. Material compatibility, proof load, temperature, coating and the governing code all require review.
B7M with A194 2HM
ASTM A193 B7M commonly uses ASTM A194 Grade 2HM. Both callouts preserve the controlled-hardness route. Dropping the “M” from the nut changes its hardness and proof-load requirements.
B7M/2HM is not automatic proof of compliance with every sour-service specification. The environment and all additional project restrictions still need to be stated.
B8 with A194 Grade 8
ASTM A193 B8 Type 304 bolting commonly uses ASTM A194 Grade 8 Type 304 nuts. The bolt class must still be stated. Grade 8 does not mean SAE J995 Grade 8 and should always be written with the ASTM A194 designation.
Class 2 or Class 2B bolting does not automatically require a strain-hardened nut. If the joint design requires a strain-hardened Grade 8 nut, ASTM A194 Supplementary Requirement S1 must be stated. S1 replaces the ordinary Grade 8 acceptance conditions with its own diameter-specific proof-load schedule and underlined marking requirement, so confirm that the selected size is covered by the current S1 tables.[1] [2]
B8M with A194 Grade 8M
ASTM A193 B8M Type 316 bolting commonly uses ASTM A194 Grade 8M Type 316 nuts. Using Grade 8 would change the nut to the Type 304 material route.
The same Class 2/S1 boundary applies: ordinary Grade 8M is the common pairing unless strain hardening is explicitly required. When S1 is invoked, do not inspect the nut against the ordinary 80 ksi proof-stress basis or ordinary Grade 8M hardness range; use the S1 schedule and marking rules. Corrosion compatibility and galling control remain design and assembly questions.
Thread and finish must agree across the assembly
For common inch-series A193 bolting, UNC is used through 1 in and 8UN above 1 in unless otherwise specified. The nut must use the matching internal thread and fit. Never pair a 1-8 UNC stud with a nut labeled only “1 in” and assume the pitch is correct.
Coated alloy-steel assemblies may need oversize-tapped nuts under the applicable coating and dimensional requirements. Stainless assemblies need controlled lubrication and tightening procedures. Put these requirements on the RFQ rather than treating them as shop-floor choices.[4]
Complete RFQ examples
Alloy-steel route: ASTM A193/A193M-26 Grade B7 studs, 1-8 UNC × 8 in, plain, 200 pcs; ASTM A194/A194M-26 Grade 2H heavy hex nuts to ASME B18.2.2, two per stud; service conditions per attached piping specification; MTR and lot traceability required.
Stainless route: ASTM A193/A193M-26 Grade B8M Class 2 studs, 3/4-10 UNC × 6 in, plain, 100 pcs; ASTM A194/A194M-26 Grade 8M heavy hex nuts to ASME B18.2.2, two per stud; lubrication per approved assembly procedure; corrosion conditions per attached datasheet; MTR and lot traceability required.
Need a bolt-and-nut set checked? Send both grade callouts, size, pitch, finish, service conditions and quantity. HexFastener can review the requested A193/A194 combination before quoting.
References
- ASTM International. ASTM A193/A193M-26. Current bolting-material specification and nut-ordering provisions.
- ASTM International. ASTM A194/A194M-26. Current companion nut specification, proof-load and supplementary requirements.
- Portland Bolt. A193 Nut Compatibility. Common A193/A194 grade pairings.
- ASTM International. ASTM A962/A962M-26. Common thread, manufacturing, testing and certification requirements invoked by A193 and A194.