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M16×2 — 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)
14 mm
Nearest inch drill: 35/64 (0.5469") · Clearance hole (normal fit): 17.5 mm ·
8.8 torque: 218 N·m dry
Thread dimensions
Major diameter
16 mm
Pitch
2 mm
TPI (equivalent)
12.7
Pitch diameter
14.701 mm
Minor diameter
13.835 mm
Tensile stress area
156.67 mm²
Tap drill sizes for M16×2
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% | 14.701 mm | 14.7 mm | 0.5781" (37/64 drill) |
| 65% | 14.311 mm | 14.3 mm | 0.5625" (9/16 drill) |
| 75% | 14.051 mm | 14 mm | 0.5469" (35/64 drill) |
| 85% | 13.792 mm | 13.8 mm | 0.5469" (35/64 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 M16×2
| Fit | Hole | Use |
|---|---|---|
| Close | 17 mm | Located joints, dowel-like alignment |
| Normal | 17.5 mm | General assembly — use this unless you have a reason not to |
| Loose | 18.5 mm | Weldments, sheet stacks, tolerance build-up |
M16×2 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 | 84.6 N·m | 63.5 N·m | 62.4 lb-ft | 26.4 kN |
| 8.8 Medium-carbon, quenched & tempered — the default structural grade | 218 N·m | 164 N·m | 161 lb-ft | 68.2 kN |
| 10.9 Alloy steel, Q&T — high strength | 312 N·m | 234 N·m | 230 lb-ft | 97.5 kN |
| 12.9 Alloy steel, Q&T — highest common grade (socket head cap screws) | 365 N·m | 274 N·m | 269 lb-ft | 114 kN |
| A2-70 304 stainless, cold worked | 169 N·m | 127 N·m | 125 lb-ft | 52.9 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
24 mm
Hex key (socket head)
14 mm