This thing is sized for a 52mm diameter DC spindle and fits on the shapeoko 2 Z-carriage. The specific spindle I designed it for was http://amzn.com/B00MN7WERA which is identical to the "quiet cut" spindle from Inventables.
The smaller hole is sized for a 1" PVC tube for vacuum purposes.
Milled from 1/2" HDPE on a shapeoko 2.
A printed version would probably work too.