This is what the shim looks like. In the thread I was reading, there have been instances where the hitch head has failed. I sure don't want that happening. There have been various versions of the head and shank and some have more clearance than others.
I believe the shims are supposed to come with your complete WDH setup but I didn't get them and never heard of them before. I thought the play was normal. I don't like the idea of tightening the bolts up to bring each side of the head together.
Reese says it's only in occasional cases where two shims are needed. I'm hope I haven't bent the head a bit to prevent two shims from fitting.