The small opening of 1.0 of your gun will lay down small paint droplets. You need to have larger droplets for primer. Primer is thicker so you need a larger opening. Prob 1.4-1.6. Your Paint data sheet should say what you need. You can but a $15 purple gun at harbor freight which comes with a 1.4 mm tip and drill it out to 1.6 if you need to ... it would take about a 1/16 inch Drill bit.
Works great.... do it all the time.
The needle is tapered so it will fit.

The last time I bought a HF gun, I had to go through about 15 to find one where the needle wasn’t rusted.

Mike


1940 Chevy 1/2 Ton presently... Almost done
1940 Chevy Business Coupe... In pieces