Universal lathe tool

[HopefulSSer]

...And there's a flange on the tailstock insert which, when the tailstock is mounted normally, takes the pressure exerted by the quill. With it backwards, the flange is pushed away from the housing and all that would hold it in would be 1 little setscrew.

(Aside: Later tailstocks had two screws. You could drill and tap yours for the second screw, symmetrical to the first.)