M20×2 thread
M20×2 tap drill
18 mm
Clearance hole 21 mm · 30 mm hex
M20×2 is a fine metric thread with a 20 mm (0.787") major diameter and 2 mm pitch. Tap it with a 18 mm drill; drill 21 mm to pass a bolt through.
The numbers
- Designation
- M20×2
- Major diameter
- 20 mm / 0.787"
- Minor diameter
- 17.835 mm
- Pitch
- 2 mm pitch
- Tap drill (75% thread)
- 18 mm — 18 mm
- Clearance hole (close fit)
- 21 mm / 0.827"
- Hex across flats
- 30 mm
How to measure what you have
- Measure across the thread crests with calipers. A used M20×2 reads a little under 20 mm — the crests are truncated by the standard, then worn and plated, so anything from about 19.6 mm up is consistent with this size.
- Measure the pitch: put a rule against the threads and count the distance over ten crests, then divide by ten. This one should give 2 mm.
- A thread pitch gauge settles it in seconds and costs very little. Guessing between a coarse and a fine thread of the same diameter is the usual way a thread gets stripped.
Tightening torque
Typical torque
375–510 N·m
276.6–376.2 lb·ft
Plain steel property class 8.8 or SAE grade 5, dry threads, tightened to about 65% of yield. Lubricated threads reach the same preload at 20-30% less torque. Where the manufacturer publishes a figure — spark plugs, wheel nuts, cylinder heads — use theirs.
Where this size turns up
- Wheel bearing and hub nuts on commercial vehicles
- Heavy adjusting screws and jacking bolts
Other threads at this diameter
| Thread | Pitch | Tap drill | Clearance |
|---|---|---|---|
| M20×2.5 | 2.5 mm | 17.5 mm | 21 mm |
| M20×1.5 | 1.5 mm | 18.5 mm | 21 mm |
Common questions
- What size drill for an M20×2 tap?
- 18 mm (18 mm), which gives about 75% thread engagement.
- What clearance hole for M20×2?
- 21 mm for a close fit — enough to pass the bolt without slop.
- What spanner fits M20×2?
- 30 mm across the flats on a standard hex head.
Related pages
Sources
- Official vendor product documentation — At One Place
- Typical range compiled from manufacturer specifications — At One Place