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3/8-inch bolt size
9/16 in wrench
across-flats spanner / socket size for 3/8 in
3/8-inch bolt — automotive and machinery.
Full specification
| System | Imperial UNC |
| Nominal diameter | 3/8 in (9.53 mm) |
| Thread pitch | 16 TPI |
| Wrench / spanner (across flats) | 9/16 in |
| Tap drill | 5/16 in (7.9 mm) |
| Clearance hole | 25/64 in |
| Common grade / class | Grade 5 |
| Typical torque | 47 Nm (35 ft·lb) |
| Closest other-system size | ~M10 |
🔧 Torque unit converter
Pre-filled with the typical torque for 3/8 in (Grade 5, dry). Edit any field to convert.
⚠️ Torque values here are general references for Grade 5 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 3/8 in
3/8-16 is a heavy general-purpose size in automotive and machinery.
A 5/16 in drill is the standard tap drill for 3/8-16.
Frequently asked questions
- What size wrench or spanner fits 3/8 in?
- 3/8-inch bolt uses a 9/16 in wrench or spanner, measured across the flats of the hex head.
- What is the torque for 3/8 in?
- A typical tightening torque for 3/8-inch bolt in Grade 5 on dry threads is about 47 Nm (35 ft·lb). Always confirm against the manufacturer spec for important joints.
- What thread pitch and tap drill does 3/8 in use?
- 3/8-inch bolt has a thread pitch of 16 TPI and uses a 5/16 in (7.9 mm) tap drill, with a 25/64 in clearance hole.