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1/4-28 UNF bolt size
7/16 in wrench
across-flats spanner / socket size for 1/4-28
1/4-28 UNF bolt — automotive and precision.
Full specification
| System | Imperial UNF |
| Nominal diameter | 1/4 in (6.35 mm) |
| Thread pitch | 28 TPI (fine) |
| Wrench / spanner (across flats) | 7/16 in |
| Tap drill | #3 (5.4 mm) |
| Clearance hole | 17/64 in |
| Common grade / class | Grade 5 |
| Typical torque | 17 Nm (12.5 ft·lb) |
| Closest other-system size | ~1/4-20 coarse |
🔧 Torque unit converter
Pre-filled with the typical torque for 1/4-28 (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 1/4-28
1/4-28 fine thread is common in automotive and precision adjustment.
1/4-28 and 1/4-20 share a 7/16 in head but the threads do not interchange.
Frequently asked questions
- What size wrench or spanner fits 1/4-28?
- 1/4-28 UNF bolt uses a 7/16 in wrench or spanner, measured across the flats of the hex head.
- What is the torque for 1/4-28?
- A typical tightening torque for 1/4-28 UNF bolt in Grade 5 on dry threads is about 17 Nm (12.5 ft·lb). Always confirm against the manufacturer spec for important joints.
- What thread pitch and tap drill does 1/4-28 use?
- 1/4-28 UNF bolt has a thread pitch of 28 TPI (fine) and uses a #3 (5.4 mm) tap drill, with a 17/64 in clearance hole.