jez
i thought you knew this ..
you need a special mech to fit that
it has no clamp , it has a plate that bolts in to a rectangular recess with two bolts
if you check the red one on e bay at the mo it has two included in the sale
and a good pic of the recess ..
SORRY JEZ IT WAS THE KIRK I WAS LOOKING AT ( head up my arse today ) although it does look like there is a recess