Fastening Know-How
Bolt Size Chart: Hex Cap Screw Dimensions, 1/4 to 1-1/2 Inch
Thread counts, wrench sizes, head heights and thread lengths for inch hex cap screws.
How to Read This Chart
- Size is the nominal diameter of the screw.
- UNC and UNF give threads per inch for the coarse and fine thread series.
- Across flats is the head width measured flat to flat, which is also the wrench or socket size.
- Minimum thread length depends on the screw length: one value for screws 6 inches and shorter, another for longer screws.
Not sure what size you have? See how to measure bolt size.
Hex Cap Screw Size Chart (Inch)
Basic dimensions for finished hex cap screws, ASME B18.2.1, with UNC and UNF threads per inch.
| Size | Decimal (in) | UNC TPI | UNF TPI | Across flats (wrench) | Head height | Min thread length, 6" and shorter | Min thread length, over 6" |
|---|---|---|---|---|---|---|---|
| 1/4" | 0.2500 | 20 | 28 | 7/16" | 5/32" | 0.750" | 1.000" |
| 5/16" | 0.3125 | 18 | 24 | 1/2" | 13/64" | 0.875" | 1.125" |
| 3/8" | 0.3750 | 16 | 24 | 9/16" | 15/64" | 1.000" | 1.250" |
| 7/16" | 0.4375 | 14 | 20 | 5/8" | 9/32" | 1.125" | 1.375" |
| 1/2" | 0.5000 | 13 | 20 | 3/4" | 5/16" | 1.250" | 1.500" |
| 9/16" | 0.5625 | 12 | 18 | 13/16" | 23/64" | 1.375" | 1.625" |
| 5/8" | 0.6250 | 11 | 18 | 15/16" | 25/64" | 1.500" | 1.750" |
| 3/4" | 0.7500 | 10 | 16 | 1-1/8" | 15/32" | 1.750" | 2.000" |
| 7/8" | 0.8750 | 9 | 14 | 1-5/16" | 35/64" | 2.000" | 2.250" |
| 1" | 1.0000 | 8 | 12 | 1-1/2" | 39/64" | 2.250" | 2.500" |
| 1-1/8" | 1.1250 | 7 | 12 | 1-11/16" | 11/16" | 2.500" | 2.750" |
| 1-1/4" | 1.2500 | 7 | 12 | 1-7/8" | 25/32" | 2.750" | 3.000" |
| 1-3/8" | 1.3750 | 6 | 12 | 2-1/16" | 27/32" | 3.000" | 3.250" |
| 1-1/2" | 1.5000 | 6 | 12 | 2-1/4" | 15/16" | 3.250" | 3.500" |
Head heights are ASME B18.2.1 basic values (1-1/2" = 15/16", checked 1 Oct 2026). Dimensions: HexCapScrews.com hex cap screw cut sheet (ASME B18.2.1) and Fastener Mart hex bolt dimension table, matched value by value (accessed 25 Sep 2026). Threads per inch: ASME B1.1 via HexCapScrews.com thread pitch chart and Wikipedia, "Unified Thread Standard" (accessed 25 Sep 2026). Heavy hex and structural bolts have different head dimensions; check the standard for those.
Related Charts and Calculators
Tighten to spec with the Grade 8 bolt torque chart, find the tap drill with the tap drill size chart, compare strength in bolt grades, or convert sizes with the metric-inch fastener converter.
Specifying a Safety-Critical Joint?
These charts are reference values drawn from published standards. Send us your drawing or specification and our team will review the fastener choice with you.