FSA Headset Bearing IS-2-138 (MR031)(37 x 48.9 x 6.5)mm – 36/45) FSA (Full Speed Ahead) headset bearings are a trusted, go-to choice for road and MTB riders. Precision-engineered with an angular contact design, they deliver smooth, reliable steering and are built to last — making them a smart, no-fuss replacement for a wide range of bikes. Outside Diameter: 48.9mm Inside Diameter: 37.0mm Height: 6.5mm Inside Angle: 36° Outside Angle: 45° TH Code: MR031 id: 37 od: 48.9 width: 6.5 mm