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#8-36 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)
#29 (0.1360")
3.5 mm · Clearance hole (normal fit): 0.1900" (#9) ·
Grade 5 torque: 2.57 lb-ft dry
Thread dimensions
Major diameter
0.164 "
Threads per inch
36
Pitch
0.706 mm
Pitch diameter
0.146 "
Minor diameter
0.1339 "
Tensile stress area
0.01473 in²
Tap drill sizes for #8-36 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% | 0.1460" | #26 (0.1470") | 3.7 mm |
| 65% | 0.1405" | #28 (0.1405") | 3.6 mm |
| 75% | 0.1369" | #29 (0.1360") | 3.5 mm |
| 85% | 0.1333" | #29 (0.1360") | 3.4 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 #8-36 UNF
| Fit | Drill | Use |
|---|---|---|
| Close | 0.1800" (#15) | Located joints, dowel-like alignment |
| Normal | 0.1900" (#9) | General assembly — use this unless you have a reason not to |
| Loose | 0.2130" (#3) | Weldments, sheet stacks, tolerance build-up |
#8-36 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 | 1.66 lb-ft | 1.25 lb-ft | 2.25 N·m | 607 lb |
| Grade 5 Medium carbon Q&T, 3 radial head marks | 2.57 lb-ft | 1.92 lb-ft | 3.48 N·m | 938 lb |
| Grade 8 Medium carbon alloy Q&T, 6 radial head marks | 3.62 lb-ft | 2.72 lb-ft | 4.91 N·m | 1,325 lb |
| 18-8 SS 304/18-8 stainless | 1.21 lb-ft | 0.906 lb-ft | 1.64 N·m | 441 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
11/32"
Hex key (socket head)
9/64