DeVilbiss CM-501 spray gun

Depends what kinda primer you wanna use with the tip size the gun has. If u take the cap off...the tip should have the size stamped in it. 1.4 is pretty common. Smaller are good for base coats and thinner viscosity coatings. Larger are good for fill primer surfaces. I paint every day and use devilbiss guns. I love them. I m not sure which model you have but chances are that its a good gun. Good luck