This is a pulley and weight hanger assembly suitable for use in a physics classroom. Designed for use with SimpleSumo robots: https://www.thingiverse.com/thing:2574286
On this setup I recommend using pennies for weights because they are standard small equal units of weight, easily available, and cheap.
The pulley uses one 608 bearing. This link is for a fidget spinner bearing which will spin with the least resistance, although you will have to protect it from dirt: http://amzn.to/2xBN9xF
Uses one 5/16" bolt to hold the assembly together.
Video of experiment involving this pulley setup shown at 6min 18 sec: