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5/8-inch lag screw size
15/16 in wrench
across-flats spanner / socket size for 5/8 in lag
5/8-inch lag screw — very heavy timber anchoring.
Full specification
| System | Imperial lag |
| Nominal diameter | 5/8 in (15.88 mm) |
| Thread pitch | coarse wood thread |
| Wrench / spanner (across flats) | 15/16 in |
| Tap drill | 3/8 in pilot |
| Clearance hole | 5/8 in |
| Common grade / class | Low-carbon steel |
| Typical torque | 160 Nm (118 ft·lb) |
| Closest other-system size | ~M16 coach |
🔧 Torque unit converter
Pre-filled with the typical torque for 5/8 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 5/8 in lag
5/8 inch lag screws anchor very heavy timber posts and beams.
Seating torque varies a lot with wood density — stop when the head pulls firmly home.
Frequently asked questions
- What size wrench or spanner fits 5/8 in lag?
- 5/8-inch lag screw uses a 15/16 in wrench or spanner, measured across the flats of the hex head.
- What is the torque for 5/8 in lag?
- A typical tightening torque for 5/8-inch lag screw in Low-carbon steel on dry threads is about 160 Nm (118 ft·lb). Always confirm against the manufacturer spec for important joints.
- What thread pitch and tap drill does 5/8 in lag use?
- 5/8-inch lag screw has a thread pitch of coarse wood thread and uses a 3/8 in pilot tap drill, with a 5/8 in clearance hole.