Use this gadget to keep track of which nozzle is actively on your printer.
You will need glue, see this video for how to orient everything.
If you just want a standalone device use:
Nozzle Indicator Bottom with Axle
Nozzle Indicator Mechanism
Nozzle Indicator Top
Nozzle Indicator Dial
Use a 0.25 mm nozzle.
All stls should be oriented correct as is.