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Yes, you can definitely get problems with the shafts not sliding smoothly onto the bearing, both from the shaft being oversized and the bearings being undersized. (I had one set of 3mm bearings that wouldn't slide over the same shaft that worked fine with a different set of 3mm bearings.) Usually, though, it is pretty easy to reduce the shaft diameter by a tiny amount with some 400 grit emory paper. I'll put the shaft in a drill and then sand a bit and then test with a bearing until the bearing will just slide over the entire length.