Bike chain sprockets

Here are two eight-tooth sprockets for standard 1/2-1/8 single-speed bicycle chain. One has a D-shaped cutout for the axle of a NEMA23 stepper motor. The other has a hexagonal cutout to take a 1/4-20 hex nut, which has a wrench size of 7/16". The OpenSCAD source code to generate these sprockets also appears here.
I am intending to use these in a homebrew stereolithographic printer. Fingers crossed.
DISCLAIMER: I originally posted these files on August 13 2014 and when I had them printed ([Sh