I like the tool holders that are mounted on the right side of the printer, but I don't like the ones that are put on top of the power supply…. The power supply on the mk3 relies on a passive cooling, so I don't like obstructing it with a tool holder on top. 

Designed specially NOT to collide with the Z axis, both the tool holder and any tools it's holding.

This one is designed to plug in to the hexagonal holes that are on the plastic parts which hold the end-screw for the Z axis. It is very stable.

Hold all of the Allen keys that came with your printer, plus the needle noose pliers that I got with mine as well (great for removing supports from printed parts btw). It also has some slots for SD cards if you like those. 

Optionally print also the small rectangular “tray” part that sits on top. Glue to the bottom part with some super glue. Nice to have for holding some smaller accessories or for a smaller IPA bottle (see the pictures and renders).

Printing

No supports needed. I printed mine in Orange PETG to match the PRUSA original parts, but you can print it however you like it, I would recommend printing it with 3+ perimeters so that it the needle-nose pliers holder part is more resilient to stresses.