I am seeking what size tubing do I need for an air assist for my Neje 3 Max.
Yes, it depends on your air pump and module air-assisted accessories. The diameter of the NEJE air-assisted air pipe is 4*3mm.
The coupling on the side of the E80 module is 4mm OD. I have this connected to an 8mm OD compressor feed via an adaptor. I used the 4mm tube to run through the cable chains, then off the side to 8mm