Threaded String Pulleys

These threaded spools have threads to keep the string from wining on top of itself, allowing for the spool radius to be constant.

There are three different spool diameters, to give you more flexibility for speed vs torque.

These spools work especially well with this kevlar line.
https://www.amazon.com/emma-kites-Strength-Activities-Tactical/dp/B07283VX4D/ref=sr_1_4?keywords=kevlar+fishing+line&qid=1554842392&s=gateway&sr=8-4