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M33×3.5 — Full Fastener Spec
ISO 68-1 / ISO 261 · Coarse series · Tap drill, clearance hole, torque, strength and tool sizes — every number on one page.
Tap drill (75% thread)
29.5 mm
Nearest inch drill: 37/32 (1.1562") · Clearance hole (normal fit): 36 mm ·
8.8 torque: 1991 N·m dry
Thread dimensions
Major diameter
33 mm
Pitch
3.5 mm
TPI (equivalent)
7.26
Pitch diameter
30.727 mm
Minor diameter
29.211 mm
Tensile stress area
693.55 mm²
Tap drill sizes for M33×3.5
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% | 30.727 mm | 30.5 mm | 1.2031" (77/64 drill) |
| 65% | 30.045 mm | 30 mm | 1.1875" (19/16 drill) |
| 75% | 29.59 mm | 29.5 mm | 1.1562" (37/32 drill) |
| 85% | 29.135 mm | 29 mm | 1.1406" (73/64 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 M33×3.5
| 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 |
M33×3.5 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 | 772 N·m | 579 N·m | 570 lb-ft | 117 kN |
| 8.8 Medium-carbon, quenched & tempered — the default structural grade | 1991 N·m | 1493 N·m | 1469 lb-ft | 301.7 kN |
| 10.9 Alloy steel, Q&T — high strength | 2849 N·m | 2137 N·m | 2102 lb-ft | 431.7 kN |
| 12.9 Alloy steel, Q&T — highest common grade (socket head cap screws) | 3330 N·m | 2498 N·m | 2456 lb-ft | 504.6 kN |
| A2-70 304 stainless, cold worked | 1545 N·m | 1159 N·m | 1139 lb-ft | 234.1 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