This attachment requires you to remove one of your existing handlebar clamp bolts. Once you have removed the bolt, measure the thread diameter and the length of the thread that goes into the handlebar.
We off three sizes of bolts
M6 = 6mm
M8 = 8mm
M10 = 10mm
The second measurement is the length of the bolt the supplied bolt lengths are approx: 55/60/65mm, once you attach the 1" ball attachment to the screw head the thread length that will go into the handlebars are approx: 27/32/37mm.