Differences In Thread Fit
For external threads the three fit classes are 1A/2A/3A and for internal thread (for example in hex nuts) 1B/2B/3B. The higher the class number the tighter the fit - 3A/3B fit therefore is the tightest and presents the greatest risk when the parts require any type of plating or additive finish. In our experience parts that require 3A/3B thread ...
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