I printed a couple other sets of these, but none would fit the pattern of screw holes on my V1 Printrbot Plus. The screws are not placed symmetrically, the 12mm shaft is not set evenly between them. This set fit my PB+ exactly. The OpenSCAD file is included.
I've added a diagram of the dimensions used for laying out the Z-Axis holes. (Which doesn't seem to show up above, here's the link: http://thingiverse-production.s3.amazonaws.com/assets/4d/d8/20/b6/4e/pb%2B_V1_Z_Holes.jpg )
I used calipers to check the dimensions on the PB+ directly.
I added a taper to the Z support shaft, I'm not very enamored with hard right angles for important support structures. That seems to be a common point of failure for my prints. Tapering or adding a fillet seems to make a big difference.
I printed these at .75 infill, .25 layer height with a .35 nozzle. First layer was 150% of the standard layer height.