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1/2-inch lag screw size
3/4 in wrench
across-flats spanner / socket size for 1/2 in lag
1/2-inch lag screw — structural timber connections.
Full specification
| System | Imperial lag |
| Nominal diameter | 1/2 in (12.7 mm) |
| Thread pitch | coarse wood thread |
| Wrench / spanner (across flats) | 3/4 in |
| Tap drill | 5/16 in pilot |
| Clearance hole | 1/2 in |
| Common grade / class | Low-carbon steel |
| Typical torque | 95 Nm (70 ft·lb) |
| Closest other-system size | ~M12 coach |
🔧 Torque unit converter
Pre-filled with the typical torque for 1/2 in lag (Low-carbon steel, dry). Edit any field to convert.
⚠️ Torque values here are general references for Low-carbon 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 1/2 in lag
1/2 inch lag screws make heavy structural timber and post connections.
A ratchet and socket beat a wrench here — lag torque builds quickly in dense wood.
Frequently asked questions
- What size wrench or spanner fits 1/2 in lag?
- 1/2-inch lag screw uses a 3/4 in wrench or spanner, measured across the flats of the hex head.
- What is the torque for 1/2 in lag?
- A typical tightening torque for 1/2-inch lag screw in Low-carbon steel on dry threads is about 95 Nm (70 ft·lb). Always confirm against the manufacturer spec for important joints.
- What thread pitch and tap drill does 1/2 in lag use?
- 1/2-inch lag screw has a thread pitch of coarse wood thread and uses a 5/16 in pilot tap drill, with a 1/2 in clearance hole.