Wolf Tooth's SDM® chainrings replace your existing spider and chainring with one clean looking, light weight, and stiff piece of machined billet. These come in 3 different offsets: standard GXP, Boost and BB30. Compatibility: - These direct mount chainrings will replace your existing chainring and spider, which is attached via 3 bolts on the back side of the spider near the spindle. You will use these same 3 bolts to attach the Wolf Tooth SDM® chainring. - There are 3 offsets: Standard: 47mm chainline, 6mm offset for cyclocross and road cranks Standard: 49mm chainline, 6mm offset for GXP and long spindle BB30 Boost: 52mm chainline, 3mm offset BB30: 49mm chainline, 0mm offset for BB30 short spindle cranks - Fat Bikes: If you are planning to use this on an X9 or XX1 fat bike crankset with a 190/197 rear hub spacing use the 0 offset ring. If your fat bike has a 170/177 rear hub spacing, use the Standard 6mm offset