Screw & Bolt Thread Size Identifier
| Nominal size | Nominal major dia. | UNC | UNF | Metric conversion |
|---|---|---|---|---|
| #0 | 0.0600 in | — | #0-80 UNF | 1.524 mm |
| #1 | 0.0730 in | #1-64 UNC | #1-72 UNF | 1.854 mm |
| #2 | 0.0860 in | #2-56 UNC | #2-64 UNF | 2.184 mm |
| #3 | 0.0990 in | #3-48 UNC | #3-56 UNF | 2.515 mm |
| #4 | 0.1120 in | #4-40 UNC | #4-48 UNF | 2.845 mm |
| #5 | 0.1250 in | #5-40 UNC | #5-44 UNF | 3.175 mm |
| #6 | 0.1380 in | #6-32 UNC | #6-40 UNF | 3.505 mm |
| #8 | 0.1640 in | #8-32 UNC | #8-36 UNF | 4.166 mm |
| #10 | 0.1900 in | #10-24 UNC | #10-32 UNF | 4.826 mm |
| #12 | 0.2160 in | #12-24 UNC | #12-28 UNF | 5.486 mm |
| 1/4" | 0.2500 in | 1/4"-20 UNC | 1/4"-28 UNF | 6.350 mm |
| 5/16" | 0.3125 in | 5/16"-18 UNC | 5/16"-24 UNF | 7.938 mm |
| 3/8" | 0.3750 in | 3/8"-16 UNC | 3/8"-24 UNF | 9.525 mm |
| 7/16" | 0.4375 in | 7/16"-14 UNC | 7/16"-20 UNF | 11.112 mm |
| 1/2" | 0.5000 in | 1/2"-13 UNC | 1/2"-20 UNF | 12.700 mm |
| 9/16" | 0.5625 in | 9/16"-12 UNC | 9/16"-18 UNF | 14.287 mm |
| 5/8" | 0.6250 in | 5/8"-11 UNC | 5/8"-18 UNF | 15.875 mm |
| 3/4" | 0.7500 in | 3/4"-10 UNC | 3/4"-16 UNF | 19.050 mm |
| 7/8" | 0.8750 in | 7/8"-9 UNC | 7/8"-14 UNF | 22.225 mm |
| 1" | 1.0000 in | 1"-8 UNC | 1"-12 UNF | 25.400 mm |
| 1-1/8" | 1.1250 in | 1-1/8"-7 UNC | 1-1/8"-12 UNF | 28.575 mm |
| 1-1/4" | 1.2500 in | 1-1/4"-7 UNC | 1-1/4"-12 UNF | 31.750 mm |
Unified scope. Designations are checked against ASME B1.1-2024 terminology and the manufacturer tables from Portland Bolt and Bolt Depot. NumPad reproduces only a limited nominal diameter–TPI directory, not ASME dimensional limits, allowances, or tolerances.
Metric scope. Terminology and basic-dimension scope follow ISO 261:1998, ISO 724:2023, and ISO 262:2023. The displayed pitch set is intentionally limited and is cross-checked with Bolt Depot’s manufacturer reference table.
Conversion. Diameter conversion uses 1 inch = 25.4 millimeters exactly, as documented by NIST. Displayed conversions are rounded to four decimal places; calculations use the unrounded conversion.
Matching method. Exact-table status uses a narrow input-rounding window: Unified diameter max(0.001 in, 0.2%) with ±0.1 TPI; metric diameter max(0.05 mm, 0.2%) with ±0.02 mm pitch. Near-match screening uses max(0.005 in, 1.5%) and ±0.6 TPI, or max(0.15 mm, 1.5%) and ±0.08 mm pitch. These are NumPad screening windows—not ASME/ISO manufacturing tolerances or inspection acceptance criteria.
Limitations. Worn or damaged crests, plating/coatings, burrs, caliper angle, internal-thread measurement, short counting spans, and pitch-gauge errors can shift readings. Diameter and pitch alone may not distinguish thread form, fit class, direction, taper, or proprietary/specialty standards.
Last verified: August 28, 2026.