Does threaded rod (all-thread) have a published straightness tolerance?
No. Standard commercial threaded rod—typically supplied in 3 ft, 6 ft, and 12 ft lengths—does not have any published or mandatory straightness tolerance.
There is no ASTM or ASME specification that assigns a default limit for straightness on fully threaded rod.
If there is no published tolerance, how is straightness handled?
According to ASME B18.31.3 (Threaded Rod Specifications):
“Straightness tolerances, when specified, shall be agreed upon by the purchaser and supplier.”
This means:
- Straightness is not automatically controlled by the spec.
- If the buyer requires a certain straightness limit, it must be written into the purchase order, and the supplier must explicitly agree to meet it.
Are there any related specifications that define straightness limits?
Yes—but only for finished studs, not long threaded rod. A stud differs from a rod in that it is measured from first thread to first thread, omitting the chamfers, and is relatively short, while a rod is measured from end to end.
The ASME B18.31.2 stud specification includes straightness limits for stud lengths up to 24 inches only.
Stud straightness requirements are as follows:
| Stud Length (Inches) | Straightness Limit |
| L ≤ 12 in | 0.006 in/in |
| 12 in < L ≤ 24 in | 0.008 in/in |
There are also metric equivalents (0.006 mm/mm and 0.008 mm/mm).
What does “0.008 in/in” mean in practical terms?
The tolerance expresses maximum deviation from straightness per inch of length.
Example:
For a 24-inch stud:
So a 24″ stud could be nearly 0.2 inches out of straightness from end to end and still meet the spec.
Can these stud tolerances be applied to long threaded rod (3–12 ft)?
Not automatically.
- ASME B18.31.2 tolerances apply only to studs, which are typically short, fully threaded or double-ended.
- Threaded rod is covered by ASME B18.31.3, which does not include any straightness values.
However, customers sometimes choose to reference the stud straightness limits as a guideline for longer rod. If so, it must be:
- Specified, and
- Agreed upon at time of order.
Because the deviation scales with length, applying 0.008 in/in to longer lengths (e.g., 144 in) could allow over 1 inch of bow, which customers often consider unacceptable unless clarified upfront.
Why isn’t straightness controlled for full-length threaded rod?
Main reasons:
- Manufacturing method
A threaded rod is typically roll-threaded from long coil-fed bars, which inherently introduces natural curvature. - Use case
Rod is commonly installed with:- Coupling nuts
- Anchor plates
- Field-cut lengths
Many applications tolerate some bow without affecting performance.
- Cost and availability
Tight straightness controls require specialty processes and significantly increase cost.
What if a project requires very straight threaded rod?
In this case, the purchaser should:
- Specify the required straightness tolerance in inches per inch (e.g., 0.005 in/in).
- Define the measurement method if critical (e.g., lay on a flat surface and measure the gap).
- Confirm supplier capability — not all mills can produce tight-tolerance rod.
- Understand that cost and lead time will increase.
What is Portland Bolt’s approach?
Generally, standard all-thread is supplied as manufactured, with no guaranteed straightness unless otherwise agreed.
If your job requires a higher degree of precision, ask an experienced Portland Bolt account manager, and we can help you get the all-thread rod you need.
