Thread Classes

Thread Classes

Thread Classes - Thread classes specify the manufacturing tolerances that are permitted. Classes 1A and 1B are for ordnance and other special applications. The letters A and B are used throughout to indicate external and internal threads, respectively. Class 2A and 2B threads are the normal production grade and are used on all standard bolts, screws and nuts. Classes 3A and 3B have minimum tolerances for applications where tight fits are required