This is a small fixture block, which is designed to be used with a fixture plate. They can be used to make any number of simple jigs and fixtures. I probably wouldn't use this to hold a part for machining, but it would be great for a drill press or assembly application.

Printing instructions and hardware links:
https://docs.google.com/document/d/1qq7KFOhIOwTGlyCK7-tqZNmj1Aby3uXWWT_-qkeeEmA/edit?usp=sharing

Sorry for separating the links into a google doc, but Thingiverse tampers with some links causing them to not work correctly.