Promax CK-1 Carbon Crankset - 175mm 2-PC Direct Mount SRAM 3-Bolt 30mm Spindle BLKPromax CK 1 Carbon Crankset 175mm 2 PC Direct Mount SRAM 3 Bolt 30mm Spindle Black. CK 1 cranks are Promaxs top of the line carbon crank offering. The race ready carbon design maximizes strength and minimizes weight. The crank arms spin on a beefy 30mm spindle to increase stiffness and power transfer. These cranks offer direct mount chainring compatibility for additional weight savings or run them with a 4 bolt 104 BCD chainring adapter available