Home › M8×1
M8×1 — Full Fastener Spec
ISO 68-1 / ISO 261 · Fine series · Tap drill, clearance hole, torque, strength and tool sizes — every number on one page.
Tap drill (75% thread)
7 mm
Nearest inch drill: J (0.2770") · Clearance hole (normal fit): 9 mm ·
8.8 torque: 27.3 N·m dry
Thread dimensions
Major diameter
8 mm
Pitch
1 mm
TPI (equivalent)
25.4
Pitch diameter
7.351 mm
Minor diameter
6.918 mm
Tensile stress area
39.17 mm²
Tap drill sizes for M8×1
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 | Metric drill | Nearest inch drill |
|---|---|---|---|
| 50% | 7.35 mm | 7.4 mm | 0.2900" (L drill) |
| 65% | 7.156 mm | 7.2 mm | 0.2812" (9/32 drill) |
| 75% | 7.026 mm | 7 mm | 0.2770" (J drill) |
| 85% | 6.896 mm | 6.9 mm | 0.2720" (I drill) |
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 M8×1
| Fit | Hole | Use |
|---|---|---|
| Close | 8.4 mm | Located joints, dowel-like alignment |
| Normal | 9 mm | General assembly — use this unless you have a reason not to |
| Loose | 10 mm | Weldments, sheet stacks, tolerance build-up |
M8×1 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 (lb-ft) | Clamp load |
|---|---|---|---|---|
| 4.6 Low-carbon steel, general purpose | 10.6 N·m | 7.93 N·m | 7.8 lb-ft | 6.6 kN |
| 8.8 Medium-carbon, quenched & tempered — the default structural grade | 27.3 N·m | 20.4 N·m | 20.1 lb-ft | 17 kN |
| 10.9 Alloy steel, Q&T — high strength | 39 N·m | 29.3 N·m | 28.8 lb-ft | 24.4 kN |
| 12.9 Alloy steel, Q&T — highest common grade (socket head cap screws) | 45.6 N·m | 34.2 N·m | 33.6 lb-ft | 28.5 kN |
| A2-70 304 stainless, cold worked | 21.2 N·m | 15.9 N·m | 15.6 lb-ft | 13.2 kN |
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
13 mm
Hex key (socket head)
6 mm