Every Hollowtech II crankset has one — that black plastic cap threaded into the end of the left crank arm that most riders forget exists until it goes missing. The Shimano Y1P417000 is the replacement, and it's the same fixing bolt that ships across a huge swath of the modern Shimano road catalog, from Ultegra 6800 down through 105 5800 and out to Sora R3000. If you've stripped the plastic hex, cross-threaded it during a swap, or pulled a used crankset off a donor bike and found the cap missing, this is the part number to order.

Function-wise, this bolt does not clamp the crank arm to the spindle — that job belongs to the two pinch bolts on the back side of the arm. What the fixing bolt does is set bearing preload. You thread it in, snug it down with the appropriate cap tool until you've taken the play out of the bottom bracket bearings, and then tighten the pinch bolts to lock the arm in place. Skip the preload step or leave the bolt out entirely and the left arm will develop lateral play no matter how hard you crank on the pinch bolts.

Compatibility is broad. The same Y1P417000 fits Ultegra FC-6800 and FC-R8000, 105 FC-5800 and FC-R7000, the newer 12-speed 105 FC-R7100, Tiagra FC-4700, Sora FC-R3000, and Claris FC-R2000, plus the RS520 road crank. If you're running a Hollowtech II road crankset from the last decade or so, odds are this is your bolt. Only one is required per crankset since only the non-drive arm uses it.... Read More