According to section 9 of the ASME B18.2.6 specification that covers fasteners for use in structural applications, an A325 structural bolt can actually be produced .12” to .25” less than the published length and still meet the specification.
According to section 9 of the ASME B18.2.6 specification, which covers dimensional tolerances for hex bolts, A325 and A490 structural bolts can actually be produced between .12 to .25 of inch less than the published length and still meet the specification.
This small difference isn’t much, but mass bolt producers save a significant amount of money in the long run by producing all of their sizes slightly shorter than the advertised length. It doesn’t make sense but that’s the way it is. The chart below outlines the allowable tolerances under ASME B18.2.6.
Bolt Length Tolerances
Structural Bolt Length Tolerance
|Nominal Length, in.
|Nominal Size, in.
|3⁄4 thru 1
|11⁄8 thru 11⁄2
|Thru 6 in.
|Over 6 in.
When considering bolt lengths for specific applications keep these length tolerances in mind. Also, remember RCSC Specification Section 2.3.2 recommends to ensure proper thread engagement the end of the bolt should be at least flush with the nut. These bolt tolerances are especially important when working with short bolt lengths. AISC offers a formula for calculating correct lengths to order bolts under Table 7-15 (7-80).