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ASME B18.31.3 Threaded Rods
Continuously threaded bars available in custom lengths, serving as versatile solutions for anchoring, hanging, and structural support systems.
ASME B18.31.3 Threaded Rods, commonly known as "all-thread" bars, are long, straight metal bars with continuous threading running along their entire length. Unlike bolts or studs which have defined lengths and head configurations, threaded rods are designed to be cut to specific lengths on-site or in the shop to suit unique application requirements. They are incredibly versatile, used extensively for hanging HVAC ductwork, electrical conduits, and piping systems from ceilings, as well as for anchoring structural elements to concrete foundations. When paired with two nuts, a threaded rod functions as a bolt; when embedded in concrete, it acts as an anchor bolt. The ASME B18.31.3 standard ensures that the thread pitch, major diameter, and straightness are consistent, allowing for reliable engagement with nuts and couplers regardless of where the rod is cut.
ASME B18.31.3 Dimensions (mm)
| Size | Nominal Diameter | Size and Threads/Inch | |||
|---|---|---|---|---|---|
| UNC | 8UN | UNF | Acme | ||
| #4 | 0.1120 | 4-40 | ... | 4-48 | ... |
| #5 | 0.1250 | 5-40 | ... | 5-44 | ... |
| #6 | 0.1380 | 6-32 | ... | 6-40 | ... |
| #8 | 0.1640 | 8-32 | ... | 8-36 | ... |
| #10 | 0.1900 | 10-24 | ... | 10-32 | ... |
| #12 | 0.2160 | 12-24 | ... | 12-28 | ... |
| 1/4 | 0.2500 | 1/4-20 | ... | 1/4-28 | 1/4-16 |
| 5/16 | 0.3125 | 5/16-18 | ... | 5/16-24 | 5/16-14 |
| 3/8 | 0.3750 | 3/8-16 | ... | 3/8-24 | 3/8-12 |
| 7/16 | 0.4370 | 7/16-14 | ... | 7/16-20 | 7/16-12 |
| 1/2 | 0.5000 | 1/2-13 | ... | 1/2-20 | 1/2-10 |
| 9/16 | 0.5620 | 9/16-12 | ... | 9/16-18 | ... |
| 5/8 | 0.6250 | 5/8-11 | ... | 5/8-18 | 5/8-8 |
| 3/4 | 0.7500 | 3/4-10 | ... | 3/4-16 | 3/4-6 |
| 7/8 | 0.8750 | 7/8-9 | ... | 7/8-14 | 7/8-6 |
| 1 | 1.0000 | 1-8 | ... | 1-12 or 1-14 UNS | 1-5 |
| 1 1/8 | 1.1250 | 1 1/8-7 | 1 1/8-8 | 1 1/8-12 | 1 1/8-5 |
| 1 1/4 | 1.2500 | 1 1/4-7 | 1 1/4-8 | 1 1/4-12 | 1 1/4-5 |
| 1 3/8 | 1.3750 | 1 3/8-6 | 1 3/8-8 | 1 3/8-12 | 1 3/8-4 |
| 1 1/2 | 1.5000 | 1 1/2-6 | 1 1/2-8 | 1 1/2-12 | 1 1/2-4 |
| 1 5/8 | 1.6250 | ... | 1 5/8-8 | ... | ... |
| 1 3/4 | 1.7500 | 1 3/4-5 | 1 3/4-8 | ... | 1 3/4-4 |
| 1 7/8 | 1.8750 | ... | 1 7/8-8 | ... | ... |
| 2 | 2.0000 | 2-4.5 | 2-8 | ... | 2-4 |
| 2 1/4 | 2.2500 | 2 1/4-4.5 | 2 1/4-8 | ... | 2 1/4-3 |
| 2 1/2 | 2.5000 | 2 1/2-4 | 2 1/2-8 | ... | 2 1/2-3 |
| 2 3/4 | 2.7500 | 2 3/4-4 | 2 3/4-8 | ... | 2 3/4-3 |
| 3 | 3.0000 | 3-4 | 3-8 | ... | 3-2 |
| 3 1/4 | 3.2500 | 3 1/4-4 | 3 1/4-8 | ... | ... |
| 3 1/2 | 3.5000 | 3 1/2-4 | 3 1/2-8 | ... | 3 1/2-2 |
| 3 3/4 | 3.7500 | 3 3/4-4 | 3 3/4-8 | ... | ... |
| 4 | 4.0000 | 4-4 | 4-8 | ... | 4-2 |
| 4 1/2 | 4.5000 | ... | ... | ... | 4 1/2-2 |
| 5 | 5.0000 | ... | ... | ... | 5-2 |
ASME B18.31.3 Dimensions (Inch)
| Size | Nominal Diameter | Size and Threads/Inch | |||
|---|---|---|---|---|---|
| UNC | 8UN | UNF | Acme | ||
| #4 | 2.845 | 4-40 | ... | 4-48 | ... |
| #5 | 3.175 | 5-40 | ... | 5-44 | ... |
| #6 | 3.505 | 6-32 | ... | 6-40 | ... |
| #8 | 4.166 | 8-32 | ... | 8-36 | ... |
| #10 | 4.826 | 10-24 | ... | 10-32 | ... |
| #12 | 5.486 | 12-24 | ... | 12-28 | ... |
| 1/4 | 6.350 | 1/4-20 | ... | 1/4-28 | 1/4-16 |
| 5/16 | 7.938 | 5/16-18 | ... | 5/16-24 | 5/16-14 |
| 3/8 | 9.525 | 3/8-16 | ... | 3/8-24 | 3/8-12 |
| 7/16 | 11.100 | 7/16-14 | ... | 7/16-20 | 7/16-12 |
| 1/2 | 12.700 | 1/2-13 | ... | 1/2-20 | 1/2-10 |
| 9/16 | 14.275 | 9/16-12 | ... | 9/16-18 | ... |
| 5/8 | 15.875 | 5/8-11 | ... | 5/8-18 | 5/8-8 |
| 3/4 | 19.050 | 3/4-10 | ... | 3/4-16 | 3/4-6 |
| 7/8 | 22.225 | 7/8-9 | ... | 7/8-14 | 7/8-6 |
| 1 | 25.400 | 1-8 | ... | 1-12 or 1-14 UNS | 1-5 |
| 1 1/8 | 28.575 | 1 1/8-7 | 1 1/8-8 | 1 1/8-12 | 1 1/8-5 |
| 1 1/4 | 31.750 | 1 1/4-7 | 1 1/4-8 | 1 1/4-12 | 1 1/4-5 |
| 1 3/8 | 34.925 | 1 3/8-6 | 1 3/8-8 | 1 3/8-12 | 1 3/8-4 |
| 1 1/2 | 38.100 | 1 1/2-6 | 1 1/2-8 | 1 1/2-12 | 1 1/2-4 |
| 1 5/8 | 41.275 | ... | 1 5/8-8 | ... | ... |
| 1 3/4 | 44.450 | 1 3/4-5 | 1 3/4-8 | ... | 1 3/4-4 |
| 1 7/8 | 47.625 | ... | 1 7/8-8 | ... | ... |
| 2 | 50.800 | 2-4.5 | 2-8 | ... | 2-4 |
| 2 1/4 | 57.150 | 2 1/4-4.5 | 2 1/4-8 | ... | 2 1/4-3 |
| 2 1/2 | 63.500 | 2 1/2-4 | 2 1/2-8 | ... | 2 1/2-3 |
| 2 3/4 | 69.850 | 2 3/4-4 | 2 3/4-8 | ... | 2 3/4-3 |
| 3 | 76.200 | 3-4 | 3-8 | ... | 3-2 |
| 3 1/4 | 82.550 | 3 1/4-4 | 3 1/4-8 | ... | ... |
| 3 1/2 | 88.900 | 3 1/2-4 | 3 1/2-8 | ... | 3 1/2-2 |
| 3 3/4 | 95.250 | 3 3/4-4 | 3 3/4-8 | ... | ... |
| 4 | 101.600 | 4-4 | 4-8 | ... | 4-2 |
| 4 1/2 | 114.300 | ... | ... | ... | 4 1/2-2 |
| 5 | 127.000 | ... | ... | ... | 5-2 |
In-Depth Engineering Reference
What materials are ASTM A193 threaded rods made from?
ASTM A193 threaded rods are most commonly supplied in Grade B7 (4140 alloy Cr-Mo, by far the most common), Grade B8M Class 1 or 2 (316 stainless for chloride/sour service), Grade B8 Class 1 or 2 (304 stainless for atmospheric service) and Grade B16 (1Cr-1Mo-¼V) for high-temperature steam service. TorqBolt also supplies B7M (NACE-compliant) and the full austenitic class-2 strain-hardened variants on customer specification.
What is the longest length of ASTM A193 threaded rod available?
Standard production lengths run up to 144 inches (12 ft); longer rods are produced on customer specification, typically by stud-end welding from coiled bar or by butt-welding two production lengths. TorqBolt manufactures both single-piece and welded threaded rods to ASME B18.31.3 dimensional tolerances.
Is ASME B18.31.3 the same as DIN 975?
Functionally similar but dimensionally different. ASME B18.31.3 is the INCH all-thread standard; DIN 975 is the metric equivalent (M3 through M52). Both cover continuous-thread rods with the full diameter threaded end to end. Conversion is by nominal thread size — for example M16-2.0 ≈ ⅝-11 UNC.
Frequently Asked Questions
- What does ASME B18.31.3 all-thread threaded rods cover?
- ASME B18.31.3 is the inch dimensional standard for all-thread threaded rods. It defines head dimensions, body diameter, thread length, total length, drive recess, and tolerances so any compliant all-thread threaded rods interchanges with standard nuts, washers and wrenches across manufacturers.
- What size range is available for all-thread threaded rods under ASME B18.31.3?
- all-thread threaded rods under ASME B18.31.3 covers 1/4 in to 4 in nominal diameter, lengths to 144 in. TorqBolt manufactures the full range in ASTM A193 Grades B7, B7M, B8, B8M and the full ASTM A320 cryogenic counterpart on customer specification.
- What is the metric/inch counterpart of ASME B18.31.3 all-thread threaded rods?
- The companion specification for all-thread threaded rods is ASME B18.31.4M metric continuous threaded studs. Both standards share equivalent functional dimensions but use the corresponding measurement system (inch vs metric ISO M-series).
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