This is a modification of a ball chain pulley, and a part to attach rolls of pennies (or other weights) to a ball chain for use as part of a Polargraph drawbot: polargraph.co.uk/
The Ball-Chain Pulley wheels are modified from "Parametric Ball Pulley" by zignig (http://www.thingiverse.com/thing:1322) to fit some old stepper motors I had and the chain I am using, and be able to mount then from the back of the board.
The small, quick-printing, and versatile second part is made to attach weights (I use rolls of pennies) to a ball chain using zip ties. It is parametric, so you can measure your ball-chain and zip ties. This is a simple replacement for "Weight for swinging pendulum" by Bre (http://www.thingiverse.com/thing:17016)