Inserts are classified as two general types: those held in place by external threads and those that use some means other than threads (knurls, grooves, interference fit) for their holding power.

We have all done it, overtightened a bolt and blown out the threads. When a bolt starts to tighten up and then go suddenly loose, you know that the threads are toast and now you have a problem.

This article was updated May 25, 2023. It was originally published Nov. 17, 2009. To put hard, durable threaded holes in plastics, engineers often specify threaded metal inserts that will securely ...