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M2.5×0.45 — 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)
2.05 mm
Nearest inch drill: #46 (0.0810") · Clearance hole (normal fit): 2.9 mm ·
8.8 torque: 0.738 N·m dry
Thread dimensions
Major diameter
2.5 mm
Pitch
0.45 mm
TPI (equivalent)
56.44
Pitch diameter
2.208 mm
Minor diameter
2.013 mm
Tensile stress area
3.39 mm²
Tap drill sizes for M2.5×0.45
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% | 2.208 mm | 2.2 mm | 0.0860" (#44 drill) |
| 65% | 2.12 mm | 2.1 mm | 0.0820" (#45 drill) |
| 75% | 2.062 mm | 2.05 mm | 0.0810" (#46 drill) |
| 85% | 2.003 mm | 2 mm | 0.0785" (#47 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 M2.5×0.45
| Fit | Hole | Use |
|---|---|---|
| Close | 2.7 mm | Located joints, dowel-like alignment |
| Normal | 2.9 mm | General assembly — use this unless you have a reason not to |
| Loose | 3.1 mm | Weldments, sheet stacks, tolerance build-up |
M2.5×0.45 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 | 0.286 N·m | 0.215 N·m | 0.211 lb-ft | 0.6 kN |
| 8.8 Medium-carbon, quenched & tempered — the default structural grade | 0.738 N·m | 0.553 N·m | 0.544 lb-ft | 1.5 kN |
| 10.9 Alloy steel, Q&T — high strength | 1.06 N·m | 0.791 N·m | 0.778 lb-ft | 2.1 kN |
| 12.9 Alloy steel, Q&T — highest common grade (socket head cap screws) | 1.23 N·m | 0.925 N·m | 0.91 lb-ft | 2.5 kN |
| A2-70 304 stainless, cold worked | 0.572 N·m | 0.429 N·m | 0.422 lb-ft | 1.1 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)
2 mm