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M33×2 — 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)
31 mm
Nearest inch drill: 39/32 (1.2188") · Clearance hole (normal fit): 36 mm ·
8.8 torque: 2184 N·m dry
Thread dimensions
Major diameter
33 mm
Pitch
2 mm
TPI (equivalent)
12.7
Pitch diameter
31.701 mm
Minor diameter
30.835 mm
Tensile stress area
760.8 mm²
Tap drill sizes for M33×2
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% | 31.701 mm | 31.5 mm | 1.2344" (79/64 drill) |
| 65% | 31.311 mm | 31.5 mm | 1.2344" (79/64 drill) |
| 75% | 31.051 mm | 31 mm | 1.2188" (39/32 drill) |
| 85% | 30.792 mm | 31 mm | 1.2188" (39/32 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 M33×2
| Fit | Hole | Use |
|---|---|---|
| Close | 34 mm | Located joints, dowel-like alignment |
| Normal | 36 mm | General assembly — use this unless you have a reason not to |
| Loose | 38 mm | Weldments, sheet stacks, tolerance build-up |
M33×2 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 | 847 N·m | 636 N·m | 625 lb-ft | 128.4 kN |
| 8.8 Medium-carbon, quenched & tempered — the default structural grade | 2184 N·m | 1638 N·m | 1611 lb-ft | 330.9 kN |
| 10.9 Alloy steel, Q&T — high strength | 3126 N·m | 2344 N·m | 2305 lb-ft | 473.6 kN |
| 12.9 Alloy steel, Q&T — highest common grade (socket head cap screws) | 3653 N·m | 2740 N·m | 2694 lb-ft | 553.5 kN |
| A2-70 304 stainless, cold worked | 1695 N·m | 1271 N·m | 1250 lb-ft | 256.8 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
50 mm
Hex key (socket head)
24 mm