When you can't tap threads in your mounting surface, push these spring plungers into unthreaded holes. They work well in wood, plastic, and other soft materials that might crack if you try to cut threads. The spring-loaded ball compresses when a part presses against it, and then pops out into a notch or groove to hold the part in place.

For a snug fit, use an arbor press to install these spring plungers in a slightly smaller hole than the body diameter.