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.
12 58 34 thru 1 118 thru 112
Thru 6 in. -0.12 -0.12 -0.19 -0.25
Over 6 in. -0.19 -0.25 -0.25 -0.25

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).

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    There are tolerances for the bolt overall length, but is there a tolerance for the actual THREAD length ? This can also makes a difference whether a said bolt length fit or not a particular situation. thank you.

    @Patrick- ASME B18.2.6 does not specifically define the thread length tolerance in the same way that they do other dimensions. Instead they control the grip gauging length and the body length with table 2 in B18.2.6 that defines both dimensions as a function of both diameter and length.

    @Sai- We are sorry, but TC bolts are not available that long. 6″ long is the maximum available. Heavy hex bolts however, are available 10″ long.

    Which is strong er, galvanized or carbon 3/4 bolts. What is the shear factor of a 2 1/2″ galvanized bolt? Houston in Va

    @Houston- There should be no difference in strength between plain and galvanized bolts, assuming both are the same grade. As for the shear strength, shear is typically calculated at 60% of tensile.

    I have a manufacturer that made very large glulam beam with custom steel connectors and installed all grade 5 plain SAE J429 bolts and a hex nut in lieu of the engineer’s stated requirement of High Strength ASTM A325. They are connected by each side with a 1/2 inch steel plate and the glulam is sandwiched inbetween. Now that they are done, they want me to take them, but I don’t want anything inferior. The supplier of the bolts said that they are a hex bolt commonly used in threaded sleeves and because they are only tested by SAE, they said never use in building or construction. What is the code answer about this? I see the IBC Referenced Standards in chapter 35 does not even mention the SAE as any referenced standard, and that is what the suppliert said, it is not ever suppose to be construction since it is not tested in the same way. Please comment. When we buy our own connectors, we use you, Mike at sales is great. Please answer asap, thanks, Sherrie Parker

    @sb parker – We do not recommend making any substitutions without the approval of an engineer. Although SAE J429 Grade 5 and ASTM A325 are similar in their strength properties, they may differ in their configuration. A325 is specified as a heavy hex structural bolt, which gives the bolt a larger bearing surface under the head. Grade 5 bolts are supplied with a finished hex head. In addition, the required hardness values differ slightly between grade 5 and A325. If any substitution were to be made, the correct bolt to substitute would be an ASTM A449 heavy hex bolt, since it is identical in its strength properties, but without the thread length limitation of A325. I would caution that you avoid deviating from the engineer’s plans without their approval and always seek written approval before proceeding with a substitution.

    Minor correction to the dimensional spec for A325 and A490 Heavy Hex Structural Bolts. The dimensions for these bolts are covered by ASME B18.2.6. This standard was created for structural application fasteners and first issued 1996. The dimensions for these bolts was removed from ANSI B18.2.1 (now ASME B18.2.1) in 1996. Note B18.2.6 is currently a 2006 revision.

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