I have a bunch of M3 to M6 threaded inserts and each manufacturer seems to have a different outside diameter/profile.  Wanted a way to test what hole size would work the best for each without having to clean out the threads from excessive melted plastic.  Came up with this model. 

It has holes from 5.5mm to 7.2mm in diameter in 0.1mm increments.  This seemed to cover all of the insert types I have.  It's 100mm X 30mm X 10mm.  I've been printing it with 3 or 4 walls and 4 or 5 top and bottom layers to ensure inserts have enough plastic to melt/bite into. 

Wasn't too concerned about pull strength, shear, etc... with this model.  There's a lot of Youtube videos going over that sort of thing.