Need new e3 Pro nozzle

PartsBuilt is the current supplier of parts for the Robo3D printers. Look here: https://www.partsbuilt.com/e3/
If you do not see the part contact the PartsBuilt folks via their web site and see if they can get them. Most likely they are some sort of standard nozzle formfactor, but I do not have one to check.

 

By too tiny I assume you mean the nozzle threads, not the nozzle extrusion diameter (which is what the 0.4 mm is referring to). If the nozzle diameter IS too small, they come in many sizes and you can try another larger one (0.8 or even larger).

If the threads that secure the nozzle into the heat sink are too small -- not sure which style the E3 uses but contact PartsBuilt and they may know. There are a few different styles of nozzles that FDM printers use and some are manufacturer specific (MakerBot is famous for that). I do not have an E3 to refer to -- perhaps @Geof can chime in if he is still listening

 

The stock one was:

• Nozzle diameter
  0.4 mm nozzle

So that is what you get if you want to stay the way it was.
If you do go with a larger nozzle diameter you will likely need to experiment with slicer settings (things like extruder feed speed and movement speed) to tune it back in. Larger diameter nozzles can make more sturdy prints (since it is thicker for each layer) but if you just want to get back to printing without fiddling -- use the 0.4

P.S. the 1.75 mm filament diameter is normal, some printers use 3 mm, but it is more a function of the extruder than the nozzle itself. The lines of filament extruded are determined by the output nozzle diameter