Adjustable Volume Straw Pipette (simpler plunger)

This pipette is based on http://www.thingiverse.com/thing:64977 but with a few modifications.

You can see the pipette in action here: https://www.youtube.com/watch?v=nqb27um8KTk

One important modification was to remove the threaded bolt from the plunger, and redesign the plunger so that a long (75mm) M4 bolt could be inserted through the length of the plunger replacing the original thread (see the detailed picture of the plunger). The thumb gears have also been modified to accept the M