Promax PI-1 Alloy Sealed Bearing 1" Press in Headset BlackPromax PI 1 Alloy Sealed Bearing 1" Press in Headset Black. The PI 1 Alloy 4545 headset has an aluminum top cap upper bearing cover lower race and upper and lower cups. All aluminum construction results in a lightweight headset. Each headset is fitted with super smooth rolling precision 4545 angular contact sealed bearings. Because this versatile headset has 4545 angular contact bearings you can use the included cups and install it in standard frames.