Bicycle headset sealed bearings(short for ACB: Angular Contact Bearing). Most of ACB made of chrome steel 100Cr6 rings & balls with double-sealed or single-seald. Some bearings made of stainless steel SUS440 with ceramic Si3N3/ZrO2 balls. These bearings application for 1", 1-1/8", 1-1/4" and 1-1/2" internal and semi integrated headsets. Mainly used in FSA, VP, HOPE, CHRIS KING, CANE CREEK, TANGE, NECO, FIRST, TOKEN, ZERONINE, RITCHEY brand headsets.