Dura-Ace cranksets went through a mid-production revision in 2013 that changed the thread depth in the left crank arm, which means two different fixing bolt lengths exist for the FC-9000 series. This B-Type bolt with its 16mm thread length fits FC-9000 cranksets manufactured after June 1, 2013, where Shimano deepened the internal threads from 8mm to 13mm. If your Dura-Ace crank dates from that era, you need to verify which version you have before ordering a replacement.

The fixing bolt sets bearing preload during left crank arm installation. Thread it into the arm using the TL-FC16 tool, tighten until lateral play disappears from the spindle, then back off slightly to avoid loading the bearings. Once the two pinch bolts are torqued to spec, the fixing bolt stays in place as a dust cap. The plastic construction is intentional since the splined interface and tool design limit how much torque you can apply, preventing overtightening that would preload the bearings incorrectly.

Compatibility extends to the FC-R9100 Dura-Ace crankset that followed the 9000 series, which uses the same 16mm thread depth. The FC-6800 Ultegra crankset also accepts this bolt, sharing the deeper thread specification with post-2013 Dura-Ace production. If you have an early FC-9000 crankset or an FC-7900, those require the shorter A-Type bolt with 8.5mm threads instead. Mixing bolt lengths won't cause immediate problems, but the wrong length either won't seat properly or won't engage enough threads for reliable retention.