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 larger than 2″ 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.
Hello Mr.Mackinnon
What are the percentages of permissible of weight of hot rolled and mild plain in accordance with ASTM? I’ve have been searching for it but still don’t get it. Hope to hear from you as soon as possible.
@Melinda- We are not aware of published weight variation values for steel. You are able to use the permissible dimension variations and calculate weight differentials, but that would only be theoretical.
Hello Mr.McKnnon
What are the allowable tolerance in length for round bars under 1500mm in length?
@Albahrani- Per ASTM A6, the only discussion of length tolerance is for hot cut steel bars. Bars 5-10 feet long (1524mm-3048mm) and up to 1″ diameter have a tolerance of -0/+1/2″. For larger diameters the tolerance widens. However, for cold cut or sheared bars, there is no tolerance listed. You will need to contact your supplier and discuss with them what their capabilities are and what the tolerances might be for different steel grades. Example, A307 and F1554 have their own tolerances listed in the respective standard.