What are the tolerances for round bar?
The bars we use to manufacture your bolts are rolled by the steel mill with standard tolerances for diameter, out of roundness, and straightness. ASTM A6 covers many of these tolerances, as well as the chemical and dimensional tolerances for other shapes and plates. Because round bar is what we primarily use, we will stick to that for the purposes of this FAQ. Further details can be found through ASTM at ASTM.org, or by contacting one of our inside salespeople.
| Specified Size, inches | Permitted Variation, Over, inches | Permitted Variation, Under, inches | Permitted Out-of-Round, inches |
|---|---|---|---|
| Up to 5/16 | 0.005 | 0.005 | 0.008 |
| Over 5/16 up to 7/16 | 0.006 | 0.006 | 0.009 |
| Over 7/16 up to 5/8 | 0.007 | 0.007 | 0.010 |
| Over 5/8 up to 7/8 | 0.008 | 0.008 | 0.012 |
| Over 7/8 up to 1 | 0.009 | 0.009 | 0.013 |
| Over 1 up to 1-1/8 | 0.010 | 0.010 | 0.015 |
| Over 1-1/8 up to 1-1/4 | 0.011 | 0.011 | 0.016 |
| Over 1-1/4 up to 1-3/8 | 0.012 | 0.012 | 0.018 |
| Over 1-3/8 up to 1-1/2 | 0.014 | 0.014 | 0.021 |
| Over 1-1/2 up to 2 | 1/64 | 1/64 | 0.023 |
| Over 2 up to 2-1/2 | 1/32 | 0 | 0.023 |
| Over 2-1/2 up to 3-1/2 | 3/64 | 0 | 0.035 |
| Over 3-1/2 up to 4-1/2 | 1/16 | 0 | 0.046 |
| Over 4-1/2 up to 5-1/2 | 5/64 | 0 | 0.058 |
| Over 5-1/2 up to 6-1/2 | 1/8 | 0 | 0.070 |
| Over 6-1/2 up to 8-1/4 | 5/32 | 0 | 0.085 |
| Over 8-1/4 up to 9-1/2 | 3/16 | 0 | 0.100 |
| Over 9-1/2 up to 10 | 1/4 | 0 | 0.120 |
As you can see in the above table, once bars get larger than 2” in diameter, the tolerance is plus only. This means that steel bars 2” and larger will always be at least their nominal size, and usually larger.
As for straightness, bars are permitted to vary ¼” in every five feet of length. So a 20 foot bar could theoretically bend as much as one inch and still be within allowable tolerances. Additionally, hot rolled bars that have been heat treated are not subject to these tolerances, but rather the straightness tolerances of their respective standards.
