instead of thinning out the rod:
1. clamp a metal loop to the rod and then hang your fixture from the loop, use a standard pipe clamp.
2, increase the diameter of the hole, said rod is inserted into, much easier with a dremmel, than thinning off the rod.
3, get a thinner rod from home depot and bend it yourself.
lots of things you can do to make it fit.
(the dremmel can thin out the rod, you just need to use a fixed clamp to hold the dremmel in place, then you move the rod over the wheel, rather than vice versa.)