Home › M42×3
M42×3 — 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)
39 mm
Nearest inch drill: 49/32 (1.5312") · Clearance hole (normal fit): 45 mm ·
8.8 torque: 4407 N·m dry
Thread dimensions
Major diameter
42 mm
Pitch
3 mm
TPI (equivalent)
8.47
Pitch diameter
40.051 mm
Minor diameter
38.752 mm
Tensile stress area
1205.98 mm²
Tap drill sizes for M42×3
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% | 40.051 mm | 40 mm | 1.5781" (101/64 drill) |
| 65% | 39.467 mm | 39.5 mm | 1.5625" (25/16 drill) |
| 75% | 39.077 mm | 39 mm | 1.5312" (49/32 drill) |
| 85% | 38.687 mm | 38.5 mm | 1.5156" (97/64 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 M42×3
| Fit | Hole | Use |
|---|---|---|
| Close | 43 mm | Located joints, dowel-like alignment |
| Normal | 45 mm | General assembly — use this unless you have a reason not to |
| Loose | 48 mm | Weldments, sheet stacks, tolerance build-up |
M42×3 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 | 1709 N·m | 1282 N·m | 1261 lb-ft | 203.5 kN |
| 8.8 Medium-carbon, quenched & tempered — the default structural grade | 4407 N·m | 3305 N·m | 3250 lb-ft | 524.6 kN |
| 10.9 Alloy steel, Q&T — high strength | 6306 N·m | 4730 N·m | 4651 lb-ft | 750.7 kN |
| 12.9 Alloy steel, Q&T — highest common grade (socket head cap screws) | 7370 N·m | 5527 N·m | 5436 lb-ft | 877.3 kN |
| A2-70 304 stainless, cold worked | 3419 N·m | 2564 N·m | 2522 lb-ft | 407 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
65 mm
Hex key (socket head)
32 mm