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 is the official technical partner of multiple World Tour and downhill 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 →.