Pulley for Serpentine Belt, customizable for poly-V (J, L, M)

This is a customizable family of poly-V pulleys for multi-rib belts, such as the serpentine belt on a car, a clothes dryer, a vacuum cleaner, a treadmill, etc... See https://en.wikipedia.org/wiki/Belt_(mechanical)#Multi-groove_belts for some uses.

The diameter, bore, number of ribs, belt profile J, L, or M), and the stub with the M3 grub-screw nut-trap are all customizable. Drop an M3 nut into the trap, and thread through it with an M3 to get a solid attachment to the shaft.

Shown is a Poly-V J4 pulley with a pitch diameter of 20mm still attached to the printbed, with a 230J3 belt hemostat clamped around its grooves.