What is the Difference between ASTM A194 Grades 2H and 2HM Nuts?
A194 2H nuts are a common high strength nut used with many different bolt grades, including A193 Grade B7, A325, A490, F1554 Grade 105 and others. Occasionally Portland Bolt will be asked to provide A194 Grade 2HM nuts, most often with A193 Grade B7M. In many grades an ‘M’ refers to metric, which is not the case here. Below is a list of similarities and differences between the two grades.
Testing
The main difference between 2H and 2HM nuts is in the testing. 2H nuts only require a hardness test on a small sample:
| Lot Size | Samples |
|---|---|
| Up to 800 | 1 |
| 801 to 8000 | 2 |
| 8001 to 22,000 | 3 |
| Over 22,000 | 5 |
2HM nuts require 100% of nuts to be hardness tested. The tests for 2HM nuts must also take into consideration 3 additional things during testing:
- Protect legibility of markings
- Minimize exterior dimensional changes
- Maintain thread fit
Chemical Composition
Both 2H and 2HM nuts have the same chemical composition.
Hardness Requirements
| Grade | Completed Nuts | Sample Nut After Heat Treat | |||
|---|---|---|---|---|---|
| Brinell Hardness | Rockwell Hardness, C Scale | Rockwell Hardness, B Scale | Brinell Hardness, min | Rockwell B Scale, Min | |
| 2H through 1½ ” | 248 to 327 | 24 to 35 | — | 179 | 89 |
| 2H over 1½ ” | 212 to 327 | 35 max | 95 min | 147 | 79 |
| 2HM | 159 to 235 | — | 84 to 99 | 159 | 84 |
Proof Load
Grade 2H nuts have a higher proof load requirement. While not showing all of the sizes, this is a representative sample.
| Nominal Size, in. | Proof Load, lbf | ||
|---|---|---|---|
| Stress Area in.2 | Grade 2HM, Heavy Hex | Grade 2H, Heavy Hex | |
| ½ | .1419 | 21,800 | 24, 830 |
| 5/8 | .226 | 33,900 | 39, 550 |
| ¾ | .334 | 50,100 | 58, 450 |
| 7/8 | .462 | 69,300 | 80, 850 |
| 1 | .606 | 90,900 | 106,000 |
Marking
| Grade and Type | Nuts Hot-Forged or Cold-Punched | Nuts Machined from Bar Stock |
|---|---|---|
| 2H | 2H | 2HB |
| 2HM | 2HM | 2HMB |
An underline as a marking requirement has been removed from 2HM but is permitted.
If you have any questions about ASTM A194 Grades 2H or 2HM nuts, give one of our experienced team members a call, and we will be happy to help you out.
Buenos días…..Puedo usar Espárragos B7M con tuerca 2H
@Rodrigo- Usually 2HM nuts are used with B7M studs since they are of similar strength and have similar testing requirements. If you’d like to make a substitution, you would need to get approval from the engineer of record for your project.
Hola buen día, si tengo unas tuercas en 2h, es correcto utilizar arandelas F436 con estas? pude revisar en otro pagina de internet que también existen arandelas en grado 2h.
@Teresa- Sí, generalmente los grados de pernos que usan tuercas 2H también recomiendan arandelas F436.
FISICAMENTE SE PUEDE NOTAR LA DIFERENCIA ENTRE B7 Y B7M, O 2H Y 2HM..??
@Ruben- B7M y 2HM tienen menor resistencia y deben marcarse en consecuencia.
Necesario e importante información para el desarrollo del trabajo con calidad y garantía
Congratuletion
If the bolts is B7 and the nuts installed is 2HM in term of quality and strength of materials during bolt torquing have no effect or any significants regarding this matter?
@Rey- A194 gr.2HM nuts are not the typically mated nut with B7 (normally 2H). However, the minimum proofload for 2HM nuts is 150ksi, so it should have sufficient strength to work properly with B7 bolts. As for the torque, that is not an easy question since torque is notoriously unpredictable. We wouldn’t think that there would be much difference between 2HM nuts and 2H nuts, but skidmore testing could verify that.