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1-1/8-12 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)
67/64 (1.0469")
26.5 mm · Clearance hole (normal fit): 1.2190" (1-7/32) ·
Grade 5 torque: 890 lb-ft dry
Thread dimensions
Major diameter
1.125 "
Threads per inch
12
Pitch
2.117 mm
Pitch diameter
1.0709 "
Minor diameter
1.0348 "
Tensile stress area
0.85572 in²
Tap drill sizes for 1-1/8-12 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% | 1.0709" | 69/64 (1.0781") | 27 mm |
| 65% | 1.0546" | 67/64 (1.0469") | 27 mm |
| 75% | 1.0438" | 67/64 (1.0469") | 26.5 mm |
| 85% | 1.0330" | 33/32 (1.0312") | 26 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 1-1/8-12 UNF
| Fit | Drill | Use |
|---|---|---|
| Close | 1.1560" (1-5/32) | Located joints, dowel-like alignment |
| Normal | 1.2190" (1-7/32) | General assembly — use this unless you have a reason not to |
| Loose | 1.3120" (1-5/16) | Weldments, sheet stacks, tolerance build-up |
1-1/8-12 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 | 397 lb-ft | 298 lb-ft | 538 N·m | 21,179 lb |
| Grade 5 Medium carbon Q&T, 3 radial head marks | 890 lb-ft | 668 lb-ft | 1207 N·m | 47,492 lb |
| Grade 8 Medium carbon alloy Q&T, 6 radial head marks | 1444 lb-ft | 1083 lb-ft | 1958 N·m | 77,014 lb |
| 18-8 SS 304/18-8 stainless | 481 lb-ft | 361 lb-ft | 653 N·m | 25,671 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
1-11/16"
Hex key (socket head)
7/8