When I tried putting my Thule bike rack in the trailer hitch of my SUV, it fits but it's wobbly. I measured the dimensions of each. The trailer hitch receiver is 53mm (ie a square 50mm each side), and the Thule bike rack is 50mm. So the fit is not tight at all. The bike rack can wobble quite a bit inside the trailer hitch. So there's 3mm of space that must be addressed. Is there a sleeve of some sort that I can buy in order to fix this issue?