MAN4MACHINE2-1/2-12 UN
Unified National (Constant Pitch)
Past the diameters UNC and UNF tables cover, threads are specified by picking a constant pitch (commonly 4, 6, 8, 12, 16, or 20 TPI) and holding it across a whole range of larger diameters, rather than looking up one fixed TPI per size. Used on large bolts, threaded rod, and machine parts where a specific TPI needs to carry across several diameters.
- Standard
- ASME B1.1
- Flank angle
- 60° included
- TPI
- 12
- Major diameter
- 2.5000" (basic)
Thread profile
A 60 degree included flank angle.
Basic major 2.5000", pitch diameter 2.4459", minor diameter 2.4098" -- theoretical dimensions before any tolerance class is applied.
UN sizes
| Size | TPI | Major Ø | Pitch Ø | Minor Ø |
|---|---|---|---|---|
| 1 | 8 | 1.0000" | 0.9188" | 0.8647" |
| 1 | 12 | 1.0000" | 0.9459" | 0.9098" |
| 1-1/8 | 8 | 1.1250" | 1.0438" | 0.9897" |
| 1-1/8 | 12 | 1.1250" | 1.0709" | 1.0348" |
| 1-1/4 | 8 | 1.2500" | 1.1688" | 1.1147" |
| 1-1/4 | 12 | 1.2500" | 1.1959" | 1.1598" |
| 1-3/8 | 8 | 1.3750" | 1.2938" | 1.2397" |
| 1-3/8 | 12 | 1.3750" | 1.3209" | 1.2848" |
| 1-1/2 | 8 | 1.5000" | 1.4188" | 1.3647" |
| 1-1/2 | 12 | 1.5000" | 1.4459" | 1.4098" |
| 1-3/4 | 8 | 1.7500" | 1.6688" | 1.6147" |
| 1-3/4 | 12 | 1.7500" | 1.6959" | 1.6598" |
| 2 | 8 | 2.0000" | 1.9188" | 1.8647" |
| 2 | 12 | 2.0000" | 1.9459" | 1.9098" |
| 2-1/4 | 8 | 2.2500" | 2.1688" | 2.1147" |
| 2-1/4 | 12 | 2.2500" | 2.1959" | 2.1598" |
| 2-1/2 | 8 | 2.5000" | 2.4188" | 2.3647" |
| 2-1/2 | 12 | 2.5000" | 2.4459" | 2.4098" |
| 2-3/4 | 8 | 2.7500" | 2.6688" | 2.6147" |
| 2-3/4 | 12 | 2.7500" | 2.6959" | 2.6598" |
| 3 | 8 | 3.0000" | 2.9188" | 2.8647" |
| 3 | 12 | 3.0000" | 2.9459" | 2.9098" |
| 3-1/4 | 8 | 3.2500" | 3.1688" | 3.1147" |
| 3-1/2 | 8 | 3.5000" | 3.4188" | 3.3647" |
| 4 | 8 | 4.0000" | 3.9188" | 3.8647" |
Did you know
A wartime supply problem, solved by treaty
American, British, and Canadian forces fighting side by side in the Second World War discovered their fasteners often didn't interchange -- American and British national thread standards had drifted apart since Sellers and Whitworth. In 1948, the three nations signed the Unified Screw Thread Agreement, creating the Unified National (UNC/UNF) series so Allied equipment and spare parts could finally interchange.
Unified Screw Thread Agreement, 1948Tap drill calculator
Try “1/4-20 UNC-2A”, “#10-32 UNF”, or “1-8 UN-3A”. Add “LH” for a left-hand thread.
Basic (theoretical) dimensions and a shop tap drill only -- ASME B1.1's exact Class 1A/2A/3A pitch diameter limits depend on length of thread engagement as well as grade. Consult the standard or a calibrated thread gauge for gauge-critical work.
Calculated live
Basic dimensions
- Major diameter
- 2.5000"
- Pitch diameter
- 2.4459"
- Minor diameter
- 2.4098"
Clearance (normal)
- Clearance drill
- 2" (2.5313")
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