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M5×0.8 — 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)
4.2 mm
Nearest inch drill: #19 (0.1660") · Clearance hole (normal fit): 5.5 mm ·
8.8 torque: 6.17 N·m dry
Thread dimensions
Major diameter
5 mm
Pitch
0.8 mm
TPI (equivalent)
31.75
Pitch diameter
4.48 mm
Minor diameter
4.134 mm
Tensile stress area
14.18 mm²
Tap drill sizes for M5×0.8
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% | 4.48 mm | 4.5 mm | 0.1770" (#16 drill) |
| 65% | 4.324 mm | 4.3 mm | 0.1695" (#18 drill) |
| 75% | 4.221 mm | 4.2 mm | 0.1660" (#19 drill) |
| 85% | 4.117 mm | 4.1 mm | 0.1610" (#20 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 M5×0.8
| Fit | Hole | Use |
|---|---|---|
| Close | 5.3 mm | Located joints, dowel-like alignment |
| Normal | 5.5 mm | General assembly — use this unless you have a reason not to |
| Loose | 5.8 mm | Weldments, sheet stacks, tolerance build-up |
M5×0.8 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 | 2.39 N·m | 1.79 N·m | 1.77 lb-ft | 2.4 kN |
| 8.8 Medium-carbon, quenched & tempered — the default structural grade | 6.17 N·m | 4.63 N·m | 4.55 lb-ft | 6.2 kN |
| 10.9 Alloy steel, Q&T — high strength | 8.83 N·m | 6.62 N·m | 6.51 lb-ft | 8.8 kN |
| 12.9 Alloy steel, Q&T — highest common grade (socket head cap screws) | 10.3 N·m | 7.74 N·m | 7.61 lb-ft | 10.3 kN |
| A2-70 304 stainless, cold worked | 4.79 N·m | 3.59 N·m | 3.53 lb-ft | 4.8 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
8 mm
Hex key (socket head)
4 mm