UPDATE:

I added a version 2 with a second mounting plate option. The new design allows you to clamp the plate in a bike stand for sturdier mounting when pulling a chain through it. It still includes a hole for a carabiner so you can use it either way, or simply use the hole/carabiner option for storage. 

This is based on a pulley system Dave Rome shared on Escape Collective to help break in a freshly waxed bike chain. He mounted his pulley's on the side of a work bench by the looks of it, and I wanted something I could move around or loan out to friends if needed. So I designed the plate the pulley wheels and cog mount to that can but hung up by a simple carabiner.

The cog was orinally split in half and intended to be printed in two parts then glued together to avoid messy supports. If you have an AMS and can print with PETG with PLA supports, I found this gives pretty good results. I've included both options in case you want to print with or without supports. I've also merged the bearing spacer into one piece for the cog part so it is in line with the other 2 pulley wheels. 

I've used this now several times with success. No more having to break in your fancy waxed chain on the first 20 minutes of your ride. 

You will need: 

5x 608 bearings (skateboard bearing), each Pulley wheel requires 2 bearing, and 1 for the cog. 

3x M6 20mm screws 

1 Carabiner