spray gun tip size

For the majority of uses, the "standard" tip size on a spray gun is typically dependent on the means of feeding paint to the tip. For a gravity feed, full sized gun, a "standard" tip size would be 1.4mm and that size tip would normally be the one supplied with the gun. A similar suction feed gun would normally be supplied with a 1.8mm tip and a similar pressure feed gun would normally use a 1.1mm tip. There are variations on this for special purposes of course, but you should be able to get a decent color coat with the "standard" tip. If you can't, I'd look to other reasons for the problem; such as reduction (thinning) in accordance with the paint manufacturer's recommendations and/or proper adjustment of air pressure to the gun. I am assuming, of course, that you are referring to a compressor-supplied gun and not a turbine gun or an airless arrangement.

Rod