A friend asked me to design and print a pulley for his model yacht for the strings which control the sail. The intention is to have a pulley wheel enclosed between two "top hat" pieces which are designed to minimise friction (would be even less with bearings but this design is too small for that).
Note that the (inverted) upper top hat sits inside the lower top hat like a sleeve and the pulley wheel runs around the outside of the lower top hat like an axle.
As always, having done this I am posting the final result and the OpenSCAD file in case it is useful for anyone else.
Obviously the pulleys can be used for other things depending on materials etc used.
There are two pulley wheel types, one with a V cross section which is more tolerant of string / rope diameter and one with a U cross section which is less tolerant but keeps the string in a more controlled location as it runs around the pulley.
The internal diameter (set carefully by the inner diameter of the upper top hat) is suitable for up to a 3.5mm screw but obviously could be changed using the OpenSCAD if you want a different one. If you want to make it bigger then make sure you have enough wall left on both top hats and that they still fit (with allowance for movement) inside the pulley wheel.