Type A for flat or slightly curved top tubes  Maximum curve of up to 3mm drop 12mm from the centre line. Most carbon and aluminium bikes require type A. The base of Type A has a flat centre with curved 'wings' that flex to the top tube profile, including going all the way flat.

 

Type B for round and heavily curved top tubes. Works on round tubes of 34mm, smaller diameters will require the mount being clamped in place overnight in order to ensure a good bond.