What is the difference between A194 Grade 4 and A194 Grade 7 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 (aka steel used to manufacture). 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. As far back as 2014, the ASTM Committee that covers the A194 specification planned to phase out Grade 4 and explicitly stated the substitutability of Grade 7 for Grade 4. In 2017, Grade 4 nuts were removed from the A194 specification.
Difference in Chemical Requirements 1
|Grade||Carbon %||Manganese %||Chromium %||Molybdenum %|
- Per ASTM A194/A194M-13