With the age of these cars the original plastic is becoming very brittle. In many cases as you remove and install parts to service your car the threads in the plastic will break rendering a costly trim piece all but worthless. These parts are intended to help save those parts and make them usable once again. There are two different types of parts, there's one that goes over a cracked thread and keeps it from breaking more, an the other is for completely replacing broken threads. The replacement piece comes in many lengths. You can always use a longer one and sand it down if there isn't a perfectly sized one.

I print these in solid ABS, and just use generous amount of superglue to hold them in place, but they can also be epoxied or plastic welded. These are all designed so that no supports are needed. Happy printing.