Spring endcap for Bertho extruder

Bertho's extruder (Thing 26094) is a great improvement for the ultimaker which requires a pretty solid spring.

The one I got happened to have a diameter of a little over a centimetre, and when you place this around a 3M bolt it can easily move off centre.

This 'end cap' is designed to thread over the 3M bolt and surround the end of the spring to keep it centred.

Simple parametric script incase anyone wants to fiddle to fit a different sized spring.