Theoretical thread dimensions
Single-start 60° profile. Approximate basic values without tolerance-class allowances; these are not acceptance limits or tap-drill diameters.
- Basic pitch diameter
- 7.1881 mm
- Approx. external minor Ø
- 6.4664 mm
- Triangle height H
- 1.0825 mm
016.75 mm arithmetic versus a 6.8 mm drill
Subtracting 1.25 from 8 gives 6.75 mm; the consulted cut-tapping table recommends 6.8 mm. A geometric shortcut is not a commercial drill size or a finished-part acceptance limit.
02Coarse M8 versus fine M8
M8 × 1 shares the nominal diameter but has a different pitch. Confirm thread spacing before replacing a screw or repairing a hole. A nut engaging for part of a turn does not prove compatibility.
03Producing a repeatable thread
Keep the entry aligned, manage chip evacuation and choose a tap suited to a through or blind hole. For production inspection, use the gauge for the required tolerance class and monitor tool wear.
Similar threads: check diameter and pitch
A fine-pitch M8 keeps the nominal diameter but changes the pitch, drill and fit. Check the full drawing designation.
| Thread | Ø mm | Pitch |
|---|---|---|
| M8 × 1.25 | 8 | 1.25 mm |
| M8 × 1 | 8 | 1 mm |
Frequently asked questions · M8 × 1.25
Which drill is used for M8 × 1.25?
The consulted cutting-tap reference specifies 6.8 mm. Form tapping requires a separately checked hole size.
What is the pitch of M8 × 1.25?
Pitch is 1.25 mm. For a single-start thread this is also the axial travel per revolution.
Does the drill size determine finished tolerance?
No. The drill prepares the hole; the tool, process and specified tolerance class determine the fit to be inspected.
Sources and standard reference
Cutting-tap drill:
VÖLKEL · Metric cutting tapsISO 68-1 · Metric thread profile
Nominal reference data. The drawing, tolerance class and tool instructions govern hole preparation and acceptance. Do not automatically use a cutting-tap drill size for form tapping.
Last updated: