Bicycle Headset

30mm For 25.4 Straight Tube Fork
34mm For 28.6 Straight Tube Fork
42mm For 28.6 Straight Tube Fork
44mm For 28.6 Straight Tube Fork
44-50.6mm For 28.6 Tapered Tube Fork
41.8-52mm For 28.6 Tapered/ Straight Tube Fork
44-56mm For 28.6 Tapered / Straight Tube Fork

For example 44-50.6mm Headset: for 44mm upper headset frame head tube ID, 50.6mm lower headset head tube ID, suitable for 28.6 Tapered Tube Fork.