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M1.6×0.35 — 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)
1.25 mm
Nearest inch drill: 3/64 (0.0469") · Clearance hole (normal fit): 1.8 mm ·
8.8 torque: 0.177 N·m dry
Thread dimensions
Major diameter
1.6 mm
Pitch
0.35 mm
TPI (equivalent)
72.57
Pitch diameter
1.373 mm
Minor diameter
1.221 mm
Tensile stress area
1.27 mm²
Tap drill sizes for M1.6×0.35
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% | 1.373 mm | 1.4 mm | 0.0550" (#54 drill) |
| 65% | 1.304 mm | 1.3 mm | 0.0520" (#55 drill) |
| 75% | 1.259 mm | 1.25 mm | 0.0469" (3/64 drill) |
| 85% | 1.214 mm | 1.2 mm | 0.0469" (3/64 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 M1.6×0.35
| Fit | Hole | Use |
|---|---|---|
| Close | 1.7 mm | Located joints, dowel-like alignment |
| Normal | 1.8 mm | General assembly — use this unless you have a reason not to |
| Loose | 2 mm | Weldments, sheet stacks, tolerance build-up |
M1.6×0.35 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 | 0.069 N·m | 0.051 N·m | 0.051 lb-ft | 0.2 kN |
| 8.8 Medium-carbon, quenched & tempered — the default structural grade | 0.177 N·m | 0.133 N·m | 0.13 lb-ft | 0.6 kN |
| 10.9 Alloy steel, Q&T — high strength | 0.253 N·m | 0.19 N·m | 0.187 lb-ft | 0.8 kN |
| 12.9 Alloy steel, Q&T — highest common grade (socket head cap screws) | 0.296 N·m | 0.222 N·m | 0.218 lb-ft | 0.9 kN |
| A2-70 304 stainless, cold worked | 0.137 N·m | 0.103 N·m | 0.101 lb-ft | 0.4 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 key (socket head)
1.5 mm