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M30×3.5 — 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)
26.5 mm
Nearest inch drill: 67/64 (1.0469") · Clearance hole (normal fit): 33 mm ·
8.8 torque: 1463 N·m dry
Thread dimensions
Major diameter
30 mm
Pitch
3.5 mm
TPI (equivalent)
7.26
Pitch diameter
27.727 mm
Minor diameter
26.211 mm
Tensile stress area
560.59 mm²
Tap drill sizes for M30×3.5
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% | 27.727 mm | 27.5 mm | 1.0781" (69/64 drill) |
| 65% | 27.045 mm | 27 mm | 1.0625" (17/16 drill) |
| 75% | 26.59 mm | 26.5 mm | 1.0469" (67/64 drill) |
| 85% | 26.135 mm | 26 mm | 1.0312" (33/32 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 M30×3.5
| Fit | Hole | Use |
|---|---|---|
| Close | 31 mm | Located joints, dowel-like alignment |
| Normal | 33 mm | General assembly — use this unless you have a reason not to |
| Loose | 35 mm | Weldments, sheet stacks, tolerance build-up |
M30×3.5 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 | 568 N·m | 426 N·m | 419 lb-ft | 94.6 kN |
| 8.8 Medium-carbon, quenched & tempered — the default structural grade | 1463 N·m | 1097 N·m | 1079 lb-ft | 243.9 kN |
| 10.9 Alloy steel, Q&T — high strength | 2094 N·m | 1570 N·m | 1544 lb-ft | 349 kN |
| 12.9 Alloy steel, Q&T — highest common grade (socket head cap screws) | 2447 N·m | 1835 N·m | 1805 lb-ft | 407.8 kN |
| A2-70 304 stainless, cold worked | 1135 N·m | 851 N·m | 837 lb-ft | 189.2 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
46 mm
Hex key (socket head)
22 mm