I published my tripod mount ring for camera lenses. This is the one I posted about before.
It’s made with OpenSCAD and has support for Customizer. There are presets for all the Canon and Nikon rings I could source dimensions for. There are also presets for using a T-nut, threaded insert, hex nut, or bare plastic (yikes!) to receive the tripod/monopod screw. The clamp can be toggled to the other side. Index marks at 90 degree intervals help align your camera quickly.
There are premade STLs for all the known ring sizes, but they all assume 1/4" x 5/16" T-nuts for mounting. You’ll want to print it in a material that resists deformation. I had bad luck with PLA and good luck with PETT (t-glase).
http://www.thingiverse.com/thing:2277236