Ratchet Wrench 14mm + 8mm

Bike workshop service runs across two crank-bolt drive formats on most days. The 14 mm socket end of the 1621-1 fits the traditional square-taper crank bolt's 14 mm hex head; the 8 mm hex end fits the ISIS / Octalink-style splined crank bolts that take an 8 mm hex driver. Two formats, one ratchet, no tool change mid-install.

The 1621-1 in the 14 mm + 8 mm cut is built for that mixed workflow. 3/8" drive on both ends, 75-tooth ratchet engagement on both, sized to the actual install and removal job a crank service runs through.

What the 8 mm hex covers

ISIS and Octalink crank bolts use an M15 splined fastener engaged by an 8 mm hex driver; that's the standard drive for Shimano Octalink (FC-M952, FC-7700 series), Truvativ / FSA ISIS-drive cranks, and most other splined-spindle square-taper cousins. The 8 mm hex also fits the broader population of M8-class hex-recessed fasteners across the bike (some pedal axle service caps, some crank-bolt service variants), so the ratchet covers more than one job on a workshop bench.

Sibling product

The Ratchet Wrench 14 mm + 15 mm covers the classic vintage square-taper workflow with the 14 or 15 mm hex-head crank bolt convention. The two ratchets share the same body and 75-tooth engagement; on a shop bench that sees both vintage square-taper and ISIS / Octalink builds, running both is the move that keeps every install in single-wrench territory.

Compatibility

• ISIS / Octalink splined crank bolts (M15 splined, 8 mm hex drive)
• Traditional square-taper crank bolts on the 14 mm socket side
• Other M8-class hex-recessed fasteners across the bike
• Any 3/8" drive socket for general use (sockets are interchangeable on the ratchet body)

Specs

• Drive: 3/8" square drive
• Ratchet engagement: 75 teeth (~4.8° arc per tooth)
• Head sizes: 14 mm socket + 8 mm hex bit, integrated to the ratchet body
• Material: premium flex plus carbon steel, hardened and tempered
• Surface finish: trivalent chrome plated per ISO 1456:2009
• Includes: the dual-head ratchet itself

Built in Zreče

Unior has been forging hand tools in Zreče since 1919, and is the official technical partner of multiple World Tour and downhill teams. The 14 + 8 mm cut is the side of the 1621 family that handles the ISIS / Octalink crank-bolt format alongside traditional square-taper hardware; one ratchet covering both engagements is the call that keeps the install from needing a second tool.

Pro tip from our mechanics

When an ISIS or Octalink crank bolt has been over-torqued or has corroded into the spindle, the 8 mm hex recess can strip before the bolt breaks loose; the recess depth and the hex tip's contact area aren't sized for breakaway torque on a seized bolt. If the wrench starts to slip in the recess, stop. Reach for a heavier-grip hex driver (or a hex-on-impact tool), engage the recess at full depth, and apply load slowly. A stripped 8 mm hex on a crank bolt is one of the most annoying recoveries in a workshop; the prevention is feeling the slip early and switching tools.

For the crank removal procedure with puller selection: How to remove a crankset →.