ACB518K Double Sealed Bicycle Headset Bearing 40x51.8x8mm, 36/45 DegreeACB518K Sealed Bicycle Headset Bearing Angular Contact 36 45 Degree 40mm x 51. 8mm x 8mm The ACB518K is a double sealed angular contact bearing designed specifically for integrated bicycle headsets. With a 36 45 degree contact angle and precision machined chrome steel construction, it provides smooth steering, long lasting support, and protection from water, dirt, and grime. Sold as one bearing. Size: 40mm ID x 51. 8mm OD x 8mm width Type: Angular