hole size ,imperial hex bolts are 1/2 inch bihex metric 13mm ,makes a difference which caliper you get as holes are sliding fitno idea what the difference is james.
yepi know bugger all of use to anyone.
its fairly imporant you get righ ones as far as securing bolts go ,only the bihex ones would be 13mm socketim pretty certain it was 13mm socket to remove james. 6 sided!!!!!!!!
bihex is lots of splines on head, is that right!! if so that's what's holding them all.