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1-1/4-12 UNF — Full Fastener Spec
ASME B1.1 (Unified) · Unf series · Tap drill, clearance hole, torque, strength and tool sizes — every number on one page.
Tap drill (75% thread)
75/64 (1.1719")
29.5 mm · Clearance hole (normal fit): 1.3440" (1-11/32) ·
Grade 5 torque: 1241 lb-ft dry
Thread dimensions
Major diameter
1.25 "
Threads per inch
12
Pitch
2.117 mm
Pitch diameter
1.1959 "
Minor diameter
1.1598 "
Tensile stress area
1.07295 in²
Tap drill sizes for 1-1/4-12 UNF
Percent of thread is a trade-off: 75% is the shop default because the last 25% of engagement adds only a few percent of strength while roughly doubling tapping torque. Drop to 50–65% in tough or gummy material, or for blind holes where a snapped tap means scrapping the part.
| Thread engagement | Exact | Inch drill | Nearest metric drill |
|---|---|---|---|
| 50% | 1.1959" | 77/64 (1.2031") | 30.5 mm |
| 65% | 1.1796" | 75/64 (1.1719") | 30 mm |
| 75% | 1.1688" | 75/64 (1.1719") | 29.5 mm |
| 85% | 1.1580" | 37/32 (1.1562") | 29.5 mm |
Roll (form) taps need a larger hole than cut taps — add roughly
0.4× the pitch to the 75% cut-tap drill and confirm against your tap maker's chart.
Clearance hole for 1-1/4-12 UNF
| Fit | Drill | Use |
|---|---|---|
| Close | 1.2810" (1-9/32) | Located joints, dowel-like alignment |
| Normal | 1.3440" (1-11/32) | General assembly — use this unless you have a reason not to |
| Loose | 1.4380" (1-7/16) | Weldments, sheet stacks, tolerance build-up |
1-1/4-12 UNF torque specs
Calculated with the short-form equation T = K · D · F, using K = 0.2 (plain, dry, as-received steel) and a target clamp load of 75% of proof load — the standard preload target for a reusable joint.
| Grade | Dry | Lubricated | Dry (N·m) | Clamp load |
|---|---|---|---|---|
| Grade 2 Low/medium carbon steel, unmarked head | 553 lb-ft | 415 lb-ft | 750 N·m | 26,555 lb |
| Grade 5 Medium carbon Q&T, 3 radial head marks | 1241 lb-ft | 930 lb-ft | 1682 N·m | 59,548 lb |
| Grade 8 Medium carbon alloy Q&T, 6 radial head marks | 2012 lb-ft | 1509 lb-ft | 2728 N·m | 96,565 lb |
| 18-8 SS 304/18-8 stainless | 671 lb-ft | 503 lb-ft | 909 N·m | 32,188 lb |
The nut factor K dominates this result. Zinc-plated, waxed, anti-seize
and lubricated threads all shift K between roughly 0.10 and 0.25, which is a 2.5×
spread in torque for identical preload. If preload actually matters, torque-to-yield,
angle control or a load-indicating washer beats a torque wrench every time.
Tool sizes
Hex head wrench
1-7/8"
Hex key (socket head)
7/8