V-blocks are used for holding and indexing round parts for milling or drilling. While these blocks aren't as rigid or precise as a hardened and ground steel version, they are fine for low precision cross drilling, and filing, and finishing. This block 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.