Sailing boats typically have plastic or rubber cylindrical covers for the lower part of the shrouds and stays (the wires that hold up the mast). These covers are called "Turnbuckle Boots".

Turnbuckle boots should be topped off with caps, but it is quite common to see the caps broken or missing entirely.

This thing is a replacement for those caps. It is fully parametric and printed perfectly without support.

See pictures to see the printed result on my boat.

Download the OpenSCAD source and edit to your requirements.
No special print instructions, printed fine on a RepRap Prusa Mendel without support.