These direct mount chainrings fit the HEIR cranksets . Lightweight machined aluminum construction. Determining Chain Ring Offset If your bike has 148mm rear spacing (Boost), choose 3mm chain ring offset If your bike has 135mm or 142mm rear spacing, choose 6mm chain ring offset (most kids bikes fall under this category). Compatibility These chainrings are compatible with: HEIR Direct Mount Cranks HEIR Carbon Cranks Zulu Three Zulu Four Zulu Five Bravo Two Bravo Three Bravo Four Not compatible with Alpha Series bikes.