Sometimes you just have to make it.

The snap-on adapter for our 18mm compression tester didn't have a valve core nor did it have threads to put one in (guess how we found that out). I had the snap-on rep send us a replacement, but this one didn't come with an 18mm adapter.... So I figured it was safe to assume more time would be wasted if I didn't take action.

I cut a valve stem off of an old wheel turned it down to .250" and then I drilled out the adapter to .251 and a little crazy glue.....

Having access to a lathe is invaluable.