Threads / Size reference
1 3/8-12 UNF
1 3/8-12 has a nominal outside diameter of 34.925 mm and a 2.116667 mm pitch.
34.925 mm
2.116667 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 3/8-12 vs 1 3/8-18
1 3/8-18 UNEF shares the nominal diameter but has a 1.411111 mm pitch. The pitch difference is 0.705556 mm; these are different nominal threads.
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| Property | 1 3/8-12 UNF | 1 3/8-18 UNEF |
|---|---|---|
| Nominal diameter · in | 1.375 | 1.375 |
| Nominal diameter · mm | 34.925 | 34.925 |
| Threads per inchDifferent | 12 | 18 |
| Pitch · mmDifferent | 2.116667 | 1.411111 |
All 3 options at this diameter
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| Designation | Major Ø · in / mm | TPI | Pitch · mm | Drill evidence | Next step |
|---|---|---|---|---|---|
| 1 3/8-6 UNC | 1.375 / 34.925 | 6 | 4.233333 | Equation only | Tap-drill lookup → |
| 1 3/8-12 UNF | 1.375 / 34.925 | 12 | 2.116667 | Equation only | Tap-drill lookup → |
| 1 3/8-18 UNEF | 1.375 / 34.925 | 18 | 1.411111 | Maker data needed | Tap-drill lookup → |
Tapping-hole evidence for 1 3/8-12
No reviewed chart row for 1 3/8-12 UNF
You can calculate a theoretical hole with the cited equation. It is not a stocked-drill selection or a tool-specific hole range.
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.
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