Thread Size Table
Sometimes I find I myself with a screw-thread I need to match, but a standard (metric) nut or bolt doesn't fit. It's clearly from some antediluvian thread class like BSF or UNC, but it's not always obvious which. My usual default is to drill it out and rethread or heli-coil it with a modern metric thread, but it's not always possible.
This table is intended to be a handy way to measure diameter and pitch and work out which thread you're looking at. It also includes tapping drill sizes (calculated as diameter minus pitch). Where multiple thread types have the same diameter and pitch (e.g. BSW 3/8"-16 and UNC 3/8"-16), you're on your own.
If you'd like a copy of this table as a spreadsheet in ODS, CSV or XLSX format, please get in touch (specifying your preferred format).
Only show metric threads
Only show coarse threads
Only show conduit/pipe threads
| Outer Diameter (mm) | Pitch (mm) | TPI (where relevant) | Tap Drill Size (mm) | Thread Class | Thread Name |
|---|---|---|---|---|---|
| 0.79 | 0.19 | 0.6 | BA | 16 BA | |
| 0.90 | 0.21 | 0.7 | BA | 15 BA | |
| 1.00 | 0.23 | 0.8 | BA | 14 BA | |
| 1.20 | 0.25 | 1.0 | BA | 13 BA | |
| 1.30 | 0.28 | 1.1 | BA | 12 BA | |
| 1.50 | 0.31 | 1.2 | BA | 11 BA | |
| 1.52 | 0.32 | 80 | 1.3 | UNF | UNF #0-80 |
| 1.70 | 0.35 | 1.4 | BA | 10 BA | |
| 1.85 | 0.35 | 72 | 1.6 | UNF | UNF #1-72 |
| 1.85 | 0.40 | 64 | 1.5 | UNC | UNC #1-64 |
| 1.90 | 0.39 | 1.6 | BA | 9 BA | |
| 2.00 | 0.25 | 1.8 | Metric Fine | M2×0.25 (Fine) | |
| 2.00 | 0.40 | 1.6 | Metric Coarse | M2×0.4 | |
| 2.18 | 0.40 | 64 | 1.8 | UNF | UNF #2-64 |
| 2.18 | 0.45 | 56 | 1.8 | UNC | UNC #2-56 |
| 2.20 | 0.43 | 1.8 | BA | 8 BA | |
| 2.50 | 0.35 | 2.2 | Metric Fine | M2.5×0.35 (Fine) | |
| 2.50 | 0.45 | 2.1 | Metric Coarse | M2.5×0.45 | |
| 2.50 | 0.48 | 2.1 | BA | 7 BA | |
| 2.51 | 0.45 | 56 | 2.1 | UNF | UNF #3-56 |
| 2.51 | 0.53 | 48 | 2.0 | UNC | UNC #3-48 |
| 2.80 | 0.53 | 2.3 | BA | 6 BA | |
| 2.84 | 0.53 | 48 | 2.4 | UNF | UNF #4-48 |
| 2.84 | 0.64 | 40 | 2.3 | UNC | UNC #4-40 |
| 3.00 | 0.35 | 2.7 | Metric Fine | M3×0.35 (Fine) | |
| 3.00 | 0.50 | 2.5 | Metric Coarse | M3×0.5 | |
| 3.18 | 0.58 | 44 | 2.6 | UNF | UNF #5-44 |
| 3.18 | 0.64 | 40 | 2.6 | BSW | BSW 1/8"-40 |
| 3.18 | 0.64 | 40 | 2.6 | UNC | UNC #5-40 |
| 3.20 | 0.59 | 2.7 | BA | 5 BA | |
| 3.50 | 0.35 | 3.2 | Metric Fine | M3.5×0.35 (Fine) | |
| 3.50 | 0.60 | 2.9 | Metric Coarse | M3.5×0.6 | |
| 3.51 | 0.64 | 40 | 2.9 | UNF | UNF #6-40 |
| 3.51 | 0.79 | 32 | 2.8 | UNC | UNC #6-32 |
| 3.60 | 0.66 | 3.0 | BA | 4 BA | |
| 4.00 | 0.50 | 3.5 | Metric Fine | M4×0.5 (Fine) | |
| 4.00 | 0.70 | 3.3 | Metric Coarse | M4×0.7 | |
| 4.10 | 0.73 | 3.4 | BA | 3 BA | |
| 4.17 | 0.71 | 36 | 3.5 | UNF | UNF #8-36 |
| 4.17 | 0.79 | 32 | 3.4 | UNC | UNC #8-32 |
| 4.70 | 0.81 | 3.9 | BA | 2 BA | |
| 4.76 | 0.79 | 32 | 4.0 | BSF | BSF 3/16"-32 |
| 4.76 | 1.06 | 24 | 3.8 | BSW | BSW 3/16"-24 |
| 4.83 | 0.79 | 32 | 4.1 | UNF | UNF #10-32 |
| 4.83 | 1.06 | 24 | 3.8 | UNC | UNC #10-24 |
| 5.00 | 0.50 | 4.5 | Metric Fine | M5×0.5 (Fine) | |
| 5.00 | 0.80 | 4.2 | Metric Coarse | M5×0.8 | |
| 5.30 | 0.90 | 4.4 | BA | 1 BA | |
| 5.49 | 0.91 | 28 | 4.6 | UNF | UNF #12-28 |
| 5.49 | 1.06 | 24 | 4.5 | UNC | UNC #12-24 |
| 5.56 | 1.06 | 24 | 4.5 | BSW | BSW 7/32"-24 |
| 5.56 | 0.91 | 28 | 4.7 | BSF | BSF 7/32"-28 |
| 6.00 | 0.75 | 5.3 | Metric Fine | M6×0.75 (Fine) | |
| 6.00 | 1.00 | 5.0 | BA | 0 BA | |
| 6.00 | 1.00 | 5.0 | Metric Coarse | M6×1 | |
| 6.35 | 0.91 | 28 | 5.5 | UNF | UNF 1/4"-28 |
| 6.35 | 0.98 | 26 | 5.4 | BSF | BSF 1/4"-26 |
| 6.35 | 1.27 | 20 | 5.1 | BSW | BSW 1/4"-20 |
| 6.35 | 1.27 | 20 | 5.1 | UNC | UNC 1/4"-20 |
| 7.14 | 0.98 | 26 | 6.2 | BSF | BSF 9/32"-26 |
| 7.94 | 1.06 | 24 | 6.9 | UNF | UNF 5/16"-24 |
| 7.94 | 1.15 | 22 | 6.8 | BSF | BSF 5/16"-22 |
| 7.94 | 1.41 | 18 | 6.6 | BSW | BSW 5/16"-18 |
| 7.94 | 1.41 | 18 | 6.6 | UNC | UNC 5/16"-18 |
| 8.00 | 0.75 | 7.3 | Metric Extra Fine | M8×0.75 (Extra Fine) | |
| 8.00 | 1.00 | 7.0 | Metric Fine | M8×1 (Fine) | |
| 8.00 | 1.25 | 6.8 | Metric Coarse | M8×1.25 | |
| 9.53 | 1.06 | 24 | 8.5 | UNF | UNF 3/8"-24 |
| 9.53 | 1.27 | 20 | 8.3 | BSF | BSF 3/8"-20 |
| 9.53 | 1.59 | 16 | 8.0 | BSW | BSW 3/8"-16 |
| 9.53 | 1.59 | 16 | 8.0 | UNC | UNC 3/8"-16 |
| 9.73 | 0.91 | 28 | 8.6 | BSP | BSP 1/8"-28 |
| 10.00 | 1.00 | 9.0 | Metric Extra Fine | M10×1 (Extra Fine) | |
| 10.00 | 1.25 | 8.8 | Metric Fine | M10×1.25 (Fine) | |
| 10.00 | 1.50 | 8.5 | Metric Coarse | M10×1.5 | |
| 10.29 | 0.94 | 27 | 8.6 | NPT | NPT 1/8"-27 |
| 11.11 | 1.27 | 20 | 9.9 | UNF | UNF 7/16"-20 |
| 11.11 | 1.41 | 18 | 9.8 | BSF | BSF 7/16"-18 |
| 11.11 | 1.81 | 14 | 9.3 | BSW | BSW 7/16"-14 |
| 11.11 | 1.81 | 14 | 9.3 | UNC | UNC 7/16"-14 |
| 12.00 | 1.50 | 10.5 | Metric Fine | M12×1.5 (Fine) | |
| 12.00 | 1.75 | 10.3 | Metric Coarse | M12×1.75 | |
| 12.70 | 1.27 | 20 | 11.5 | UNF | UNF 1/2"-20 |
| 12.70 | 1.41 | 18 | 11.3 | BSCon | BSCon 1/2"-18 |
| 12.70 | 1.59 | 16 | 11.2 | BSF | BSF 1/2"-16 |
| 12.70 | 1.95 | 13 | 10.8 | UNC | UNC 1/2"-13 |
| 12.70 | 2.12 | 12 | 10.6 | BSW | BSW 1/2"-12 |
| 13.16 | 1.34 | 19 | 11.5 | BSP | BSP 1/4"-19 |
| 13.72 | 1.41 | 18 | 11.1 | NPT | NPT 1/4"-18 |
| 14.00 | 1.50 | 12.5 | Metric Fine | M14×1.5 (Fine) | |
| 14.00 | 2.00 | 12.0 | Metric Coarse | M14×2 | |
| 14.29 | 1.41 | 18 | 12.9 | UNF | UNF 9/16"-18 |
| 14.29 | 1.59 | 16 | 12.7 | BSF | BSF 9/16"-16 |
| 14.29 | 2.12 | 12 | 12.2 | BSW | BSW 9/16"-12 |
| 14.29 | 2.12 | 12 | 12.2 | UNC | UNC 9/16"-12 |
| 15.88 | 1.41 | 18 | 14.5 | UNF | UNF 5/8"-18 |
| 15.88 | 1.41 | 18 | 14.5 | BSCon | BSCon 5/8"-18 |
| 15.88 | 1.81 | 14 | 14.1 | BSF | BSF 5/8"-14 |
| 15.88 | 2.31 | 11 | 13.6 | BSW | BSW 5/8"-11 |
| 15.88 | 2.31 | 11 | 13.6 | UNC | UNC 5/8"-11 |
| 16.00 | 1.50 | 14.5 | Metric Fine | M16×1.5 (Fine) | |
| 16.00 | 2.00 | 14.0 | Metric Coarse | M16×2 | |
| 16.66 | 1.34 | 19 | 15.0 | BSP | BSP 3/8"-19 |
| 17.15 | 1.41 | 18 | 14.7 | NPT | NPT 3/8"-18 |
| 17.46 | 1.81 | 14 | 15.7 | BSF | BSF 11/16"-14 |
| 17.46 | 2.31 | 11 | 15.2 | BSW | BSW 11/16"-11 |
| 18.00 | 1.50 | 16.5 | Metric Extra Fine | M18×1.5 (Extra Fine) | |
| 18.00 | 2.00 | 16.0 | Metric Fine | M18×2 (Fine) | |
| 18.00 | 2.50 | 15.5 | Metric Coarse | M18×2.5 | |
| 19.05 | 1.59 | 16 | 17.5 | UNF | UNF 3/4"-16 |
| 19.05 | 1.59 | 16 | 17.5 | BSCon | BSCon 3/4"-16 |
| 19.05 | 2.12 | 12 | 17.0 | BSF | BSF 3/4"-12 |
| 19.05 | 2.54 | 10 | 16.6 | BSW | BSW 3/4"-10 |
| 19.05 | 2.54 | 10 | 16.6 | UNC | UNC 3/4"-10 |
| 20.00 | 1.50 | 18.5 | Metric Extra Fine | M20×1.5 (Extra Fine) | |
| 20.00 | 2.00 | 18.0 | Metric Fine | M20×2 (Fine) | |
| 20.00 | 2.50 | 17.5 | Metric Coarse | M20×2.5 | |
| 20.96 | 1.81 | 14 | 18.7 | BSP | BSP 1/2"-14 |
| 21.34 | 1.81 | 14 | 18.3 | NPT | NPT 1/2"-14 |
| 22.00 | 1.50 | 20.5 | Metric Extra Fine | M22×1.5 (Extra Fine) | |
| 22.00 | 2.00 | 20.0 | Metric Fine | M22×2 (Fine) | |
| 22.00 | 2.50 | 19.5 | Metric Coarse | M22×2.5 | |
| 22.23 | 1.81 | 14 | 20.5 | UNF | UNF 7/8"-14 |
| 22.23 | 2.31 | 11 | 20.0 | BSF | BSF 7/8"-11 |
| 22.23 | 2.82 | 9 | 19.5 | BSW | BSW 7/8"-9 |
| 22.23 | 2.82 | 9 | 19.5 | UNC | UNC 7/8"-9 |
| 22.91 | 1.81 | 14 | 20.7 | BSP | BSP 5/8"-14 |
| 24.00 | 2.00 | 22.0 | Metric Fine | M24×2 (Fine) | |
| 24.00 | 3.00 | 21.0 | Metric Coarse | M24×3 | |
| 25.40 | 1.59 | 16 | 23.9 | BSCon | BSCon 1"-16 |
| 25.40 | 2.12 | 12 | 23.3 | UNF | UNF 1"-12 |
| 25.40 | 2.54 | 10 | 22.9 | BSF | BSF 1"-10 |
| 25.40 | 3.18 | 8 | 22.3 | BSW | BSW 1"-8 |
| 25.40 | 3.18 | 8 | 22.3 | UNC | UNC 1"-8 |
| 26.44 | 1.81 | 14 | 24.2 | BSP | BSP 3/4"-14 |
| 26.67 | 1.81 | 14 | 23.4 | NPT | NPT 3/4"-14 |
| 27.00 | 2.00 | 25.0 | Metric Fine | M27×2 (Fine) | |
| 27.00 | 3.00 | 24.0 | Metric Coarse | M27×3 | |
| 30.00 | 2.00 | 28.0 | Metric Fine | M30×2 (Fine) | |
| 30.00 | 3.50 | 26.5 | Metric Coarse | M30×3.5 |
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