Flask Centering Jig

This is a very specific model, but I've gotten several requests to post it here.  It is a jig designed to fit on to this magnetic mixer, and center this flask.  

The jig comes in two pieces - the base, and center.  I printed the center with a brim, and left the brim on to keep it flush (see video).   I printed this in PC, but any material should work.