I designed this Trim Potentiometer adjustment tool for adjusting a variety of different trimpot models, and it should fit most trimpot barrels.

While there is nothing wrong with this model, there is a second version here that is a little larger and includes a larger knurled knob to help with precise adjustments.

It is intended for use at a nuclear power plant, where Foreign Material Exclusion is a major concern, so it is also intended to float for easy retrieval should it be dropped into water. 

Features:

Inset flathead tweaker

Floats

Lanyard loop

Indexing points on the top and near the tip to help align the flathead with the recess in the pot.

Printing Recommendations:

Do not use supports. This will fill the internal hollow space meant to keep it floating. Necessary supports are designed into the file.

Filament: This should be printable with just about any filament other than TPU. 

Walls: 2+

Infill: Doesn't matter, it will be all walls anyway. 

USE ARACHNE WALL GENERATOR SETTINGS. "Detect Thin Walls tends to some structures not printing well. 

Layer Height: 0.12mm to .2mm, but smaller layer heights will work better. 

Post Processing:

The designed in support fin below the tip should snap off, but may be on a little more tightly and need to be cut off.