Threads / Size reference
1-20 UNEF
1-20 has a nominal outside diameter of 25.4 mm and a 1.27 mm pitch.
25.4 mm
1.27 mm pitch
Nominal dimensions; no class allowances or acceptance limits applied. Diameter is in inches; the number after the dash is TPI.
same diameter comparison
1-20 vs 1-12
1-12 UNF shares the nominal diameter but has a 2.116667 mm pitch. The pitch difference is 0.846667 mm; these are different nominal threads.
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| Property | 1-20 UNEF | 1-12 UNF |
|---|---|---|
| Nominal diameter · in | 1 | 1 |
| Nominal diameter · mm | 25.4 | 25.4 |
| Threads per inchDifferent | 20 | 12 |
| Pitch · mmDifferent | 1.27 | 2.116667 |
All 3 options at this diameter
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| Designation | Major Ø · in / mm | TPI | Pitch · mm | Drill evidence | Next step |
|---|---|---|---|---|---|
| 1-8 UNC | 1 / 25.4 | 8 | 3.175 | Chart row | Tap-drill lookup → |
| 1-12 UNF | 1 / 25.4 | 12 | 2.116667 | Chart row | Tap-drill lookup → |
| 1-20 UNEF | 1 / 25.4 | 20 | 1.27 | Maker data needed | Tap-drill lookup → |
Tapping-hole evidence for 1-20
No reviewed chart row for 1-20 UNEF
No UNEF drill row or UNEF-specific equation scope has been reviewed. Use the exact tap maker’s data; a UNC/UNF drill at the same diameter is not a substitute.
Need acceptance limits?
The complete class and applicable drawing requirements are needed. These nominal values are not maximum/minimum inspection limits.
Part has no marking?
Measure the correct diameter and pitch, then compare candidates across metric and inch systems.
Basis for this size
Nominal designation and family transcribed from the live directory on 2026-10-19; unit conversions are calculated using exactly 25.4 mm/in. No matching drill row has been reviewed for this exact size. Paid standard limit tables have not been reviewed.