Promax HF-3 Hollow Hot Forged Crankset - 172.5mm 2-PC Direct Mount SRAM 3-Bolt 30mm Spindle BLKPromax HF 3 Hollow Hot Forged Crankset 172. 5mm 2 PC Direct Mount SRAM 3 Bolt 30mm Spindle Black. HF 3 cranks are Promaxs top of the line aluminum crank offering. Hollow forged from 6061 T6 aluminum both crank arms are hollow so they are super stiff yet lightweight. The crank arms spin on a beefy 30mm spindle permanently fitted into the drive side arm. These cranks offer direct mount sprocket compatibility for additional weight savings or run them