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M27×2 — 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)
25 mm
Nearest inch drill: 63/64 (0.9844") · Clearance hole (normal fit): 30 mm ·
8.8 torque: 1164 N·m dry
Thread dimensions
Major diameter
27 mm
Pitch
2 mm
TPI (equivalent)
12.7
Pitch diameter
25.701 mm
Minor diameter
24.835 mm
Tensile stress area
495.74 mm²
Tap drill sizes for M27×2
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% | 25.701 mm | 25.7 mm | 1.0156" (65/64 drill) |
| 65% | 25.311 mm | 25.3 mm | 1.0000" (1 drill) |
| 75% | 25.051 mm | 25 mm | 0.9844" (63/64 drill) |
| 85% | 24.792 mm | 24.8 mm | 0.9688" (31/32 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 M27×2
| Fit | Hole | Use |
|---|---|---|
| Close | 28 mm | Located joints, dowel-like alignment |
| Normal | 30 mm | General assembly — use this unless you have a reason not to |
| Loose | 32 mm | Weldments, sheet stacks, tolerance build-up |
M27×2 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 | 452 N·m | 339 N·m | 333 lb-ft | 83.7 kN |
| 8.8 Medium-carbon, quenched & tempered — the default structural grade | 1164 N·m | 873 N·m | 859 lb-ft | 215.6 kN |
| 10.9 Alloy steel, Q&T — high strength | 1666 N·m | 1250 N·m | 1229 lb-ft | 308.6 kN |
| 12.9 Alloy steel, Q&T — highest common grade (socket head cap screws) | 1948 N·m | 1461 N·m | 1436 lb-ft | 360.7 kN |
| A2-70 304 stainless, cold worked | 903 N·m | 678 N·m | 666 lb-ft | 167.3 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
41 mm
Hex key (socket head)
19 mm