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 sponsors professional road and mountain-bike race 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 →.