3/8" Drive Metric Hex Bit

The 3/8" drive hex bit, sized per individual order. The middle-ground drive size for torque-wrench-controlled hex work, sitting between the 1/4" drive for small fasteners and the 1/2" drive for the high-load end. The format that covers the working-torque range most bike-relevant hex fasteners actually live in.

The 3/8" drive is the workshop default for the 20 to 60 Nm band, which is where most crank-installation, BB-tool, and chainring-bolt work happens. Pair a 3/8" drive hex bit with a 3/8" torque wrench in the right band, and you can hit the manufacturer's published spec on every hex fastener that needs torque control without swapping drive sizes mid-service.

The bit is premium carbon steel, hardened and tempered. The socket housing is chrome-vanadium, finished with trivalent chrome to ISO 1456:2009 on the non-bit surfaces. The geometry follows DIN 7422, the industry standard for hex bit socket dimensions; the bit-to-recess fit is what stops the bolt from rounding when the torque wrench clicks.

Compatibility

• 3/8" square drive: pairs with 3/8" torque wrenches in the 5–60 Nm bands and Unior's Pro Socket Handle in 3/8" drive

Each size in the 236/2HX line covers a different bike fastener cluster:

• 5 mm: stem steerer-clamp bolts; seatpost binders; saddle-rail bolts (high end of stem face-plate torque)
• 6 mm: disc-brake caliper-mount bolts (mid-band torque); some chainring bolts
• 8 mm: pedal threads from inside; some crank-fixing bolts on square-taper interfaces

For the 10 mm hex sizes that crank-spindle bolts use (Campagnolo crank work), the 3/8" Drive Long Hex Bit (236/2HXL) extends the reach into the spindle recess; the standard 236/2HX doesn't have the length for that specific job.

Specs

• 3/8" square drive
• Single hex size per bit (size selected at order)
• Premium carbon steel bit, hardened and tempered
• Chrome-vanadium socket housing
• Trivalent chrome plating to ISO 1456:2009
• Manufactured to DIN 7422 (Hex bit sockets, dimensional standard)
• Manufactured in Slovenia

Built in Zreče, Slovenia

Unior has been forging hand tools in Zreče since 1919, and sponsors professional road and mountain-bike race teams. The 3/8" drive hex line is the workshop-grade complement to the standalone hex T-handles and Y-handles, sized to pair with the same 3/8" torque wrenches a typical bike shop uses for crank and BB work.

Pro tip from our mechanics

The trick to keeping a 3/8" drive hex bit set working is to use it only on the fasteners that actually need torque-wrench control. A 5 mm hex bit run through a thousand bottle-cage bolts wears the tip faster than it would on the dozen seatpost-binder bolts a year that actually need the torque wrench. Use the T-handle for the wear-eating work; use the 3/8" drive bit for the torque-controlled work.

For when the 3/8" drive hex bit format earns its place over a T-handle or Y-handle, and the per-fastener working-torque thresholds: Hex and Torx wrenches: how to pick the right tool for the job →.