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1/4 inch set screw size
1/8 in hex key
Allen / internal hex key size for 1/4 grub
1/4 inch set screw — collars, pulleys and couplings.
Full specification
| System | Imperial (Alloy) |
| Nominal diameter | 1/4 in (6.35 mm) |
| Thread pitch | 20 TPI |
| Hex key (Allen) | 1/8 in |
| Tap drill | #7 (5.1 mm) |
| Clearance hole | n/a (threaded) |
| Common grade / class | Alloy |
| Typical torque | 8 Nm (5.9 ft·lb) |
| Closest other-system size | ~M6 |
🔧 Torque unit converter
Pre-filled with the typical torque for 1/4 grub (Alloy, dry). Edit any field to convert.
⚠️ Torque values here are general references for Alloy 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 grub
The 1/4-20 set screw is a common imperial collar and pulley fastener.
A 1/8 in hex key drives 1/4-20 set screws.
Frequently asked questions
- What size Allen / hex key fits 1/4 grub?
- 1/4 inch set screw uses a 1/8 in hex (Allen) key with an internal hex drive.
- What is the torque for 1/4 grub?
- A typical tightening torque for 1/4 inch set screw in Alloy on dry threads is about 8 Nm (5.9 ft·lb). Always confirm against the manufacturer spec for important joints.
- What thread pitch and tap drill does 1/4 grub use?
- 1/4 inch set screw has a thread pitch of 20 TPI and uses a #7 (5.1 mm) tap drill, with a n/a (threaded) clearance hole.