Threads Internal or external threads in standard systems can be molded-in or machined after molding.
Coarse threads are always desirable.
Threads finer than 28 pitch or more precise than Unified System Class 2 are preferably machined. Roots and crests of the threads must be rounded to avoid stress concentrations and to add strength. Avoid terminating threads in feather edges or against shoulders where a notch could be created and cause failure.