Genuine FSA MR121 TH870E 1-1/8 Headset Bearing, also known as 'Campy', Campag or Campagnolo.
Also fits many high end BMX frames.
Inside diameter 30.5mm
Outside Diameter 41.8mm
45 / 45 degree mounting surface angles.
Supplied in loose workshop style packaging.
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'Parts
& Accessories for Trials,Trails and Tarmac!'