ABEC--5, C3 Clearance, 15mm x 26mm x 7mm These radial cartridge bearings meet the ABEC-5 tolerance standard. They feature high precision chromium steel balls that are smooth rolling and durable. ABEC-5 radial bearing is designed specifically for bicycle applications 52100 High-Carbon Chromium alloy deep-groove design races help to promote a longer bearing life Precise long-lasting Grade 10 Balls are made from 52100 Chromium Steel 90% fill with Mobil XHP 222 high pressure water proof grease LLU seal facing outward, towards the elements, to reduce contamination from water or dirt Lighter-contact (less seal-drag) LLB seal facing inward keep the grease where it belongs