SRAM "DUB" (29mm) specific bottom bracket. Aluminum cups precisioned machined in the USA with Angular Contact ABEC 5 440C Stainless Steel Enduro Bearings. Fits standard "BSA" threaded bottom bracket shells using Left and Right cups. With the right cranks, can also be used on 100mm and 120mm FATBIKES. DUB cranks, while appearing to have 30mm spindles are undersized and require specially sized bearings (nominal 29mm). Angular contact bearings are a step forward in outboard bottom bracket design. Why? Deep groove radial ball bearing cartridges are not designed to be "adjusted." Any inward or outward pressure on the inner races put them out of alignment with the outer races, forcing the balls to ride up the side of the groove and exerting greater pressure on the races. This results in increased friction and premature wear. Since almost all outboad crank sets exert some inward pressure on the bearings when installed, it only makes sense to use a bearing designed specifically for such loads. Angular contact bearings result in 100% ball engagement when properly pre-loaded.