I thought I'd have to redo part of my project because the reviewers say they're too small an inner diameter at 5.9mm. I was surprised because I've always had good luck with their bearings. I double checked and they are indeed 6mm plus or minus 0.01mm. If people learned how to use their digital calipers properly, maybe they wouldn't post bad reviews. It measures 5.9mm internally if you depress the caliper's upper jaws just enough for the jaws to interfere with your measurements.