I hate the wheel collars because the Allen wrench set screw is never a standard size and always strips out.
Believe me, the set screw IS a standard size, imperial or metric. It is a case of getting the correct size hex key.
"c" clips are 'C' shaped clips that click into a circular slot cut around diameter of a circular rod. If the slot is cut too deep the clips will fall out, if not deep enough they will break while trying to force them in.
Ed S