Tuesday, August 21, 2018
Thread fit measures the looseness of fit between male and female threads. 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 fit are at greater risk of not passing the Go/No-Go gauge test after electroplating, especially at smaller diameters. Typically this happens because more of the plating material is added to the part at it's extremities, making a consistent plating thickness difficult to achieve and thereby compromising the tight fit tolerance at the end of the screw where the gauges engage.