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 answer to a stuck cap. Finger pressure on a small plastic thumbwheel only goes so far; seat an 8 mm hex key in the socket and you can drive the 1609.1 with real, controlled torque while your palm holds the splines pressed square into the cap. The cap comes loose; the splined drive holes don't get rounded on the way.

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. The cap itself is conventionally threaded; the reversed left-hand thread on a Hollowtech II system belongs to the drive-side bottom bracket cup, not the cap.

For a stuck or over-torqued cap, seat an 8 mm hex key in the tool's centre socket and turn the key instead of the thumbwheel. The extra leverage breaks the cap free while you keep the splines pressed fully home, so the drive holes don't round out.

Reinstall is preload only. Finger-tight plus a quarter turn (0.7 Nm recommended) 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).
• Unior's official fitment listing is Shimano Hollowtech II only; nothing else is on the datasheet, so don't count on it fitting other brands' preload caps.
• 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: moulded plastic (the chrome-plated steel version is the separate Crank Cap Tool Metal, 1609.1/2)
• Weight: 6 g listed
• Drive: splined drive on the working face matched to the Shimano Hollowtech II cap; 8 mm hex socket through the centre so an Allen key can drive the tool on stuck caps

Built in Zreče

Unior has been forging hand tools in Zreče since 1919, and sponsors professional road and mountain-bike race 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 →.

FAQ

Which cranks does the 1609.1 fit? Unior's official fitment is Shimano Hollowtech II — the standard splined preload cap used across the road and MTB groupsets. It does not fit SRAM DUB caps, which are pin-pattern (use the Crank Cap Tool for SRAM DUB), or the original XTR FC-M970 outboard-nut interface (use the 1664 crank puller).

What is the 8 mm hex hole in the middle for? It takes an 8 mm Allen key so you can drive the tool instead of finger-turning it. On a cap that is stuck or over-torqued, seat the key in the centre socket and turn the key — you get real, controlled leverage while your palm keeps the splines pressed fully into the cap's drive holes.

How tight should a Hollowtech II crank cap be? 0.7 Nm — finger-tight plus a quarter turn at most. The cap is plastic and only sets bearing preload, so over-tightening deforms it. The clamping is done by the two 5 mm hex pinch bolts on the left crank arm, tightened alternately to 12–14 Nm.

Is the plastic tool strong enough, or do I need the metal 1609.1/2? For its intended job, yes — the cap is a 0.7 Nm plastic fastener, so the forces involved are small, and the 8 mm hex socket covers stuck caps. The Crank Cap Tool Metal (1609.1/2) drives the same splined interface in chrome-plated steel — 33 g against 6 g — and adds a rear storage magnet and 13 mm wrench flats for bench use.