Here is an link to a YouTube of a automatic thread stop that I made for my 13 x 40 Jet lathe. I actually don't know why most lathes do not have one from the factory. To me it seems like it should be standard on all lathes or at least most. It lets you thread up against a shoulder on the OD where you can see the shoulder or in the ID were you can not see when to disengage the half nut lever. And it will stop within a few thousands of an inch. This idea could probably work on many other types of lathes. I thought this might very useful for all of the Model Engine Builders out there.