What is the length tolerance for a bolt?
ASME 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 | |||||
|---|---|---|---|---|---|---|
| 1⁄4 to 3⁄8 | 7⁄16 and 1⁄2 | 9⁄16 to 3⁄4 | 7⁄8 and 1 | 11⁄8 to 11⁄2 | Over 11⁄2 | |
| Up to 1 in. incl. | +0.02 -0.03 | +0.02 -0.03 | +0.02 -0.03 | - - | - - | - - |
| Over 1 in. to 21⁄2 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 21⁄2 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 | |||||
|---|---|---|---|---|---|---|
| 1⁄4 to 3⁄8 | 7⁄16 and 1⁄2 | 9⁄16 to 3⁄4 | 7⁄8 and 1 | 11⁄8 to 11⁄2 | Over 11⁄2 | |
| Up to 1 in. incl. | -0.03 | -0.03 | -0.03 | - | - | - |
| Over 1 in. to 21⁄2 in., incl. | -0.04 | -0.06 | -0.08 | -0.10 | -0.12 | -0.18 |
| Over 21⁄2 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 | |
|---|---|---|
| 1⁄2 and Smaller | Over 1⁄2 | |
| 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.
Hi, the + and – usually means that its within those dimensions, correct? So you know that 0 would be that the bolt is snug against the surface but + would mean it is not snug against the surface and – would mean that it is past the surface? Am I missing something? how is it possible to be inside the surface?
Thanks!
@Chantale- The bolt length tolerances in the FAQ are only in relation to the bolt itself. Meaning that if you order a bolt of a certain size, the actual length can vary based on these charts. It is important to understand these tolerances as you are designing your joints, but the do not really have anything to do with the actual installation or whether or not it is tightened.
Hi ,
Appriciated for exp. of What does it mean : Non-Pointed Products
@Arie- Non-pointed products means any bolt without a machined point. Examples of a machined point are lag screws, cone pointed pole-line hardware, and a few others, usually for wood applications.
The cap screw length tolerance table states the cap screws are pointed or chamfered.
What is the formula for the length of the pointed end. Typically for stud bolts, we use 1 1/2 times the pitch (threads per inch).
@Garry- ASME B18.2.1 says that the chamfer shall be between one and two thread pitches, so your 1-1/2x should be right in the middle.
Do the negative length tolerances of Hvy Hex Cap Screw have a range or are they always the value listed in the table? For instance, B18.2.1 lists the negative length tolerance as +0.00/-0.18 for a 1 1/2″ diameter x 1″ thru 2 1/2″ in length.
@Garry- Any bolt sold as meeting ASME B18.2.1, which is most ASTM or SAE cap screws, should have lengths conforming to the tolerances per table 13 of B18.2.1. Hex bolts have tolerances covered by table 5, and structural bolts like A325 or A490 should conform to the length tolerances per section 2.1.8 of ASME B18.2.6.
Have you these tolerances for the metric bolt?
@Patrick – Apologies, we do not have that information.
Are the tolerances in inch or mm ?
@Mike – These tables use imperial (inch) dimensions/tolerances