ASTM A194 Gr. 7 vs A194 Gr. 4 heavy hex nuts
While A194 Grade 4 and A194 Grade 7 nuts are mechanically identical and have the same intended applications, the only difference is the chemical values.
Grade 4 was created to be a low-cost alternative to Grade 7 by using a lower cost raw material. Unfortunately, this did not work out. The idea was that the material used to make Grade 4 was cheaper, and therefore the nuts would be cheaper.
In practice that was not the case. Since the steel used to manufacture Grade 7 nuts is mass produced and the material used to make Grade 4 was not, Grade 7 nuts remained cheaper, thus defeating the entire reason for Grade 4 to exist.
The ASTM Committee for the A194 specification planned the phase-out of Grade 4 back in 2014 and explicitly stated that Grade 7 was the replacement for Grade 4. In 2017, Grade 4 was removed from the A194 specification.
In 2017, Grade 4 nuts were removed from the A194 specification.
Difference in Chemical Requirements
| Grade | C % | Mn % | Cr % | Mo % |
| 4 | .40-.50 | .70-.90 | ... | .20-.30 |
| 7 | .37-.49 | .65-1.10 | .75-1.20 | .15-.25 |
Reference(s) .. www.portlandbolt.com
Related Post(s)
The Stud Bolt theoretical length can be calculated by means of the formula...