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5/16-inch lag screw size
1/2 in wrench
across-flats spanner / socket size for 5/16 in lag
5/16-inch lag screw — medium timber fixings.
Full specification
| System | Imperial lag |
| Nominal diameter | 5/16 in (7.94 mm) |
| Thread pitch | coarse wood thread |
| Wrench / spanner (across flats) | 1/2 in |
| Tap drill | 3/16 in pilot |
| Clearance hole | 5/16 in |
| Common grade / class | Low-carbon steel |
| Typical torque | 27 Nm (19.9 ft·lb) |
| Closest other-system size | ~M8 coach |
🔧 Torque unit converter
Pre-filled with the typical torque for 5/16 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 5/16 in lag
5/16 inch lag screws handle medium timber connections and ledger boards.
Pilot the pilot hole to about 70 percent of the shank for a strong, split-free hold.
Frequently asked questions
- What size wrench or spanner fits 5/16 in lag?
- 5/16-inch lag screw uses a 1/2 in wrench or spanner, measured across the flats of the hex head.
- What is the torque for 5/16 in lag?
- A typical tightening torque for 5/16-inch lag screw in Low-carbon steel on dry threads is about 27 Nm (19.9 ft·lb). Always confirm against the manufacturer spec for important joints.
- What thread pitch and tap drill does 5/16 in lag use?
- 5/16-inch lag screw has a thread pitch of coarse wood thread and uses a 3/16 in pilot tap drill, with a 5/16 in clearance hole.