Often, the quick solution is to use lockwashers or thread-lock compounds. A more-permanent, less-costly solution from Balax Inc., North Lake, Wis. (www.balax.com), is to thread the hole with their patented Thredlock Tap. It creates a thread geometry that incorporates a spring along the entire length of the threaded hole. As a screw is inserted, the spring clamps down and generates a prevailing torque during assembly and resists loosening. Like other forming taps, Tredlock Taps work in ductile materials such as aluminum, brass, copper, stainless, carbon and leaded steel, as well as zinc. (In general, any material which produces stringy chips are good candidates for forming taps. If chips are powdery, the material may be too brittle.) The threads can be formed for blind and thru-hole applications, and the finished tapped holes are compatible with standard, off-the-shelf fasteners.
The taps form threads by displacing metal, not cutting it. This eliminates chips and chip removal in blind holes. And for materials that work harden, such as steel and wrought aluminum, the grain flow of formed threads follows the thread contour, strengthening the thread.