Depth stops for a 5" (130mm) 3 jaw metal lathe chuck, specifically a Bison chuck. They might fit others. These stops help keep the work parallel at a specific distance from the face of the lathe chuck.
I have included STL's for stops in nominal sizes from 1/8" to 1/2" and have also included the Freecad file (0.18.4) so you can completely customize the stops however you wish.
The author hasn't provided the model origin yet.