3/8" Drive Metric Hex Bit, Long Type

The 3/8" drive hex bit with a 66 mm bit length. The format for fasteners that sit deep in a recess where a standard-length socket bottoms out before the hex engages the bolt. Specifically: 10 mm hex bolts on Campagnolo cranksets, where the bolt sits at the bottom of the spindle bore and a standard bit can't reach.

A Campagnolo crank installation is the canonical use case. The crank bolt is M14 with a 10 mm hex recess at the centre of the spindle; the spindle's depth means a short-length hex bit lacks the reach to engage the bolt while the socket housing sits clear of the crank arm. The 66 mm bit length on the 236/2HXL is sized to put the bit at the bolt while the socket housing rides above the spindle recess.

The bit is premium carbon steel, hardened and tempered. The socket is chrome-vanadium, with trivalent chrome plating on the non-bit surfaces. The longer-bit format demands tighter dimensional tolerance than a standard-length bit; any wobble at the bit-to-socket interface gets amplified across the 66 mm reach, which is why this tool's machining is held to a tighter spec than the short-bit version.

Compatibility

• 3/8" square drive: pairs with 3/8" torque wrenches in the appropriate Nm band for the fastener
• Currently shipping: 10 mm hex bit, sized for Campagnolo crank-spindle bolts
• Additional sizes scheduled in the line; check current catalog before ordering for a specific application

The crank-bolt working torque on Campagnolo crank designs typically falls in the 40–50 Nm band; a 3/8" drive torque wrench in that range plus this long-bit socket is the complete tool combination for the install.

Specs

• 3/8" square drive
• 66 mm bit length (long format)
• Currently 10 mm hex
• 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 long-bit format is the specialty version of the 3/8" drive hex line, sized to reach into the deep-recess fasteners a standard bit can't engage; the construction is the same carbon-steel bit and chrome-vanadium socket as the rest of the 236 series.

Pro tip from our mechanics

If you're not sure whether a fastener needs the long-bit format, the test is straightforward: try a standard hex bit, and if the socket housing fouls against the crank arm or the bottom-bracket shell before the bit engages the bolt, the long-bit is the right tool. The same logic applies to any deep-recess hex bolt; the long-bit format isn't Campagnolo-specific, it's deep-recess-specific.

For the deep-recess fastener layouts where a long-bit socket beats a standard bit, and the 3/8" drive band where torque-wrench control matters: Hex and Torx wrenches: how to pick the right tool for the job →.