Fine threads can be torqued to a greater amount than course threads when good material is used. They also have a greater ability to stay tight when subject to vibration or shock loads. The automotive industry uses mostly fine threads for these reasons. In soft materials however, fine threads will pull out and therefore a course thread must be used. Older bolt action rifles such as a Mauser use course threads as they are case hardened all over. If you case harden a fine thread, the thread will be all case and no tough core and will tear out. A course thread will have a hard skin but still have a tough core. Modern bolt action rifle designs such as the Browning A-Bolt (Howa) have a fine thread as they are not case hardened but locally heat treated where required.

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