1-1/2" Tapered headset bottom bearing SS MH-P21, also called SS ACB3749.
Basic size : ID 37 * OD 49 * W 7 mm (short for ¢49×7×45°)
Angle : 45°/45°
Material : stainless steel SUS440 for races and balls
Cage : PA66+25%GF
Lubrication : Mobil XHP-222
Seal : double-sealed
It is suitable for Specialized Roubaix bicycle.