Years ago machining for production was done on turret lathes. My past employeer did this also until about 15yrs ago, then when 85% mazak, but anyway... There was a tool used to do undercuts for internal threaded parts so you have a groove (recess) to install a rubber washer for the seal. To operate you run the saddle in to set your depth inside part then pull the handle on this toolholder which would raise your cutter to cut recess behind the threads. I have contacted several tooling suppliers such as Dorian and Aloris and they all are drawing a blank. Does anyone have an idea what I'm even trying to describe???? The turret lathes used were 1940's and 50's.