Summary

This design is a holder to securely hold a tip at the extremity of a micromanipulator and make precision electrical measurements. I have used it with glass capillaries for single cell measurements, sewing needles for large (>50 micron) electronic pads and tungsten tip for smaller pads.
To build this device you will need a 2mm rod, a M2 screw and a spring with an inner diameter between 6 or 7 mm and about 30mm long.
There are different versions with various hole sizes indicated by the file name.
It is designed to be compact, provide a secure attachment and allow to change the tip easily but the electrical connection should be assured by an alligator clip or a soldered wire.
To ensure stability i recommend to attach the electrical wire to the rod.

If you also want to print the micromanipulator take a look here: https://www.thingiverse.com/thing:6641450