Hollowtech II Crank Bolt Tool

If you've worked on a Shimano crank in the last fifteen years, you've handled the small splined cap tool that goes in the centre. You've also probably misplaced a couple. They're easy to drop into a parts tray, easy to lose under a workbench, and easy to find that you don't have one when you need it. The 1609.1 is that tool, with one feature that earns it a spot at the bench: an 8 mm hex socket drilled through the centre.

The hex socket is the recovery for a stuck cap. When the splined drive on the cap's outer face slips, or when the cap is over-torqued past what the splines can break loose, an 8 mm hex Allen key drops through the 1609.1 and engages the cap directly. The cap moves; the bench doesn't pick up a damaged-cap problem on top of a stuck-cap problem.

How it's used

For a routine cap removal, fit the 1609.1's splines onto the cap's outer drive holes. Press firmly down so the splines seat fully (a partial seating slips under torque and rounds the holes), then rotate counter-clockwise. Hollowtech II caps are left-hand thread on the drive side, so loosening direction is opposite the standard right-hand convention.

For a stuck or over-torqued cap, drop an 8 mm hex Allen key through the 1609.1's centre and into the cap's hex centre. The hex engages a different cross-section than the splines; the cap breaks free without rounding the splined drive holes.

Reinstall is preload only. Finger-tight plus a quarter turn (about 0.5–0.7 Nm) sets the bearing preload; over-tightening the cap deforms the plastic on most Shimano tiers. The non-drive pinch bolts (12–14 Nm per Shimano's spec) are the structural fastener.

Compatibility

• All current Shimano Hollowtech II cranks with the standard splined cap interface (Dura-Ace, Ultegra, 105, Tiagra, Sora, Claris road; XTR, XT, SLX, Deore MTB; including the current FC-M9100, FC-M8100, and FC-M7100 generations).
• SRAM GXP cranks; the GXP cap shares the splined drive with current Hollowtech II.
• Not compatible with the original FC-M970-era proprietary outboard spindle nut interface; for those, use the dedicated Crank Puller for Shimano XTR FC-M970 (1664).
• Not compatible with SRAM DUB caps (pin-pattern, not splined); for DUB, use the Crank Cap Tool for SRAM DUB.

Specs

• Material: premium flex plus carbon steel
• Surface finish: chrome-plated to ISO 1456:2009
• Drive: splined drive on the working face matched to Shimano HT2 / SRAM GXP cap geometry; 8 mm hex socket through the centre for stuck caps

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 8 mm centre hex on the 1609.1 is the workshop refinement that separates a bench tool from a parts-bag tool; it converts a stuck-cap call from “remove and replace cap” to “remove cap, reinstall cap” without any new parts.

Pro tip from our mechanics

Buy two. The 1609.1 is the tool you most reliably can't find when you need it, and at this price the spare in the tool roll prevents the moment when the bike on the stand stops being serviceable because a cap tool walked off in someone's apron.

For the HT2 cap-tool engagement procedure, the GXP-vs-HT2 distinction, and the full crank-removal sequence: How to remove a crankset →.