This is a fsa no 42 c40 acb headset as used on pinnacle arkose and dolomite alongside hoy sa calobra and alto irpavi bikes the bearing are 1 18 45 x 45 degrees upper and 15 36 x 45 degree lower angular contact bearings that sit flush in the frame with head tube outer diameter of 46 mm upper and 56 mm lower on tapered forks