What is the length tolerance for a bolt?

bolt-length-measure-heroASME B18.2.1 has a table that deals with the length tolerance for square, hex, heavy hex, and askew head bolts. It also has a section for lag screws as well as tighter tolerance cap screws. The tolerance varies greatly per diameter and length of the fastener. See the table below.

Length Tolerance for Non-Pointed Products Including Square, Hex, Heavy Hex, and Askew Head Bolts

Nominal Length Nominal Size
14 to 38 716 and 12 916 to 34 78 and 1 118 to 112 Over 112
Up to 1 in. incl. +0.02 -0.03 +0.02 -0.03 +0.02 -0.03 - - - - - -
Over 1 in. to 212 in., incl. +0.02 -0.04 +0.04 -0.06 +0.06 -0.08 +0.08 -0.10 +0.12 -0.12 +0.18 -0.18
Over 212 in. to 4 in., incl. +0.04 -0.06 +0.06 -0.08 +0.08 -0.10 +0.10 -0.14 +0.16 -0.16 +0.20 -0.20
Over 4 in. to 6 in., incl. +0.06 -0.10 +0.08 -0.10 +0.10 -0.10 +0.12 -0.16 +0.18 -0.18 +0.22 -0.22
Longer than 6 in. +0.10 -0.18 +0.12 -0.18 +0.14 -0.18 +0.16 -0.20 +0.22 -0.22 +0.24 -0.24

Length Tolerance for Pointed Products Including Hex Cap Screws (Finished Hex Bolts) and Heavy Hex Screws

Nominal Length Nominal Size
14 to 38 716 and 12 916 to 34 78 and 1 118 to 112 Over 112
Up to 1 in. incl. -0.03 -0.03 -0.03 - - -
Over 1 in. to 212 in., incl. -0.04 -0.06 -0.08 -0.10 -0.12 -0.18
Over 212 in. to 4 in., incl. -0.06 -0.08 -0.10 -0.14 -0.16 -0.20
Over 4 in. to 6 in., incl. -0.10 -0.10 -0.10 -0.16 -0.18 -0.22
Longer than 6 in. -0.18 -0.18 -0.18 -0.20 -0.22 -0.24

Length Tolerance for Hex Lag Screws

Nominal Screw Length Nominal Screw Diameter
12 and Smaller Over 12
Through 6 in. Over 6 in. ±0.12 ±0.25 ±0.25 ±0.25

ASTM A325 and A490 heavy hex structural bolts have length tolerances that are specific to these bolts only. See our FAQ addressing the length tolerances for structural bolts.

The ASTM F1554 anchor bolt specification also has a section dealing with length tolerance. See the below excerpt…

10.4.1 The overall length of straight anchor bolts, or length to the inside of the hook, shall be the specified length +/- 1⁄2 in. (13 mm) for lengths 24 in. (600 mm) or less, and +/- 1 in. (25 mm) for longer bolts.
10.4.2 The length of hooks shall be the specified length, +/-10 % of the specified hook length, or +/- 1⁄2 in. (13 mm), whichever is greater.

Since the length of anchor bolts is often a noncritical dimension, the F1554 specification has a generous length tolerance. If the F1554 anchor bolt is to be a headed bolt with a forged head, it is Portland Bolt’s interpretation of the specification that the F1554 length tolerances apply to the headed anchor bolts as well as anchor rods and 90 degree bent anchor bolt.

All-thread rod or fully threaded studs are a gray area in terms of being specifically mentioned or dealt with by a specification in terms of length tolerance. The above chart and citations deal only with headed bolts and anchor bolts respectively and do not mention studs or all thread used for general applications. Many bolt specifications simply require the purchaser to state the length tolerances to the manufacturer. Making matters worse, all-thread rod is always chamfered on the ends to facilitate easy assembly of the nuts. Sometimes threaded studs are measured from end to end, while other times they are measured “first to first”, meaning from the beginning of the first thread on each end, not the overall length of the rod. Portland Bolt manufactures construction grade fasteners; if your product or application requires tight dimensional requirements please discuss those requirements with us.

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