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M8 coach screw size
13 mm wrench
across-flats spanner / socket size for M8 coach
M8 coach screw — medium timber connections.
Full specification
| System | Metric coach |
| Nominal diameter | 8 mm |
| Thread pitch | coarse wood thread |
| Wrench / spanner (across flats) | 13 mm |
| Tap drill | 5 mm pilot |
| Clearance hole | 9 mm |
| Common grade / class | 4.6 / steel |
| Typical torque | 20 Nm (14.8 ft·lb) |
| Closest other-system size | ~5/16 in lag |
🔧 Torque unit converter
Pre-filled with the typical torque for M8 coach (4.6 / steel, dry). Edit any field to convert.
⚠️ Torque values here are general references for 4.6 / steel 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 M8 coach
M8 coach screws are a common choice for fence posts and timber brackets.
Hot-dip galvanised M8 coach screws last far longer outdoors.
Frequently asked questions
- What size wrench or spanner fits M8 coach?
- M8 coach screw uses a 13 mm wrench or spanner, measured across the flats of the hex head.
- What is the torque for M8 coach?
- A typical tightening torque for M8 coach screw in 4.6 / steel on dry threads is about 20 Nm (14.8 ft·lb). Always confirm against the manufacturer spec for important joints.
- What thread pitch and tap drill does M8 coach use?
- M8 coach screw has a thread pitch of coarse wood thread and uses a 5 mm pilot tap drill, with a 9 mm clearance hole.