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M20 bolt size
30 mm wrench
across-flats spanner / socket size for M20
M20 bolt — structural steel and large machinery.
Full specification
| System | Metric coarse |
| Nominal diameter | 20 mm |
| Thread pitch | 2.5 mm |
| Wrench / spanner (across flats) | 30 mm |
| Tap drill | 17.5 mm |
| Clearance hole | 22 mm |
| Common grade / class | 8.8 |
| Typical torque | 410 Nm (302 ft·lb) |
| Closest other-system size | ~3/4 inch |
🔧 Torque unit converter
Pre-filled with the typical torque for M20 (8.8, dry). Edit any field to convert.
⚠️ Torque values here are general references for 8.8 on clean, dry threads. Lubrication, coatings, and the joint material change the figure significantly. For structural, automotive, or safety-critical work, always use the torque specified by the manufacturer or engineer.
About M20
M20 is a heavy structural size used in steel framing and large machinery bases.
Use a long breaker bar or impact tool — M20 torque is beyond comfortable hand tightening.
Frequently asked questions
- What size wrench or spanner fits M20?
- M20 bolt uses a 30 mm wrench or spanner, measured across the flats of the hex head.
- What is the torque for M20?
- A typical tightening torque for M20 bolt in 8.8 on dry threads is about 410 Nm (302 ft·lb). Always confirm against the manufacturer spec for important joints.
- What thread pitch and tap drill does M20 use?
- M20 bolt has a thread pitch of 2.5 mm and uses a 17.5 mm tap drill, with a 22 mm clearance hole.