Outer bearings are 6 x 15 x 5mm (stock is 6 x 12 x 4mm), Inner bearings are 12 x 21 x 5mm (stock is 12 x 18 x 4mm), Wider bearings create an additional 2mm of contact with the axle for smoother, longer running performance, 3mm larger bearings have balls a full 33% larger than stock!, The load ratings of RPM oversized bearings are double that of stock bearings and more than triple the fatigue rating of stock bearings as well! SKU: RCHOB1602