Last week, I printed the 34mm bracket. Today I finished my cable chain, so I assembled everything. How tight should it be? It clips on, but keeps falling off during use. The "clip" part of it has a bit of a gap. I thought maybe I printed the wrong one, so I just did the 39mm one and that's definitely the wrong size as it won't fit at all. I also measured my damper, and it's 6mm like yours.
I printed the 34mm one at .2 with 30% infill. I'll try printing another one tomorrow in case I screwed something up.
I attached a picture of a top-down view of the X motor to show the gap on the bracket.