What *I* would do if I were to manufacture bolts I’d make them print holding the longitudinal length to a very low tolerance. For example, the print may call out 35mm +0.1mm/-0.15mm (I’m making this up). I’d insure that the dimensions are nominally 35mm and the variance WITHIN what’s allowable. In other words, QUALITY CONTROL & QUALITY ASSURANCE. Now... what DO THEY DO? I cannot imagine them deviating from what I’ve outlayed. It would be interesting to measure, say, 10 examples of Colt, BCM, LMT, etc., bolts with statistical analysis. That would make a nice technical article. Sent from my iPhone using Tapatalk