Universal adjustable Z endstop for 8mm smooth rod

This is a remix/recombination of bruckj's http://www.thingiverse.com/thing:454635

You can find a more or less editable version in Tinkercad: https://tinkercad.com/things/4gdR7HQbQSL

It uses 3mm dia 25mm and 30mm bolts with lock nuts for fixing to the smooth rod and a 4mm dia bolt for adjustment.

Try to find a strong spring that can fit in. I think pen springs might not be very usefull, but you can experiment.