Paul,

The gray primer is labeled as primer. They also make a red primer but that is more for covering bare metal as a rust preventative. The gray has more fill material and is a true sandable primer. It can be sanded wet or dry and has the same qualities as any good auto primer that you would find in an auto paint store. But, none of the hassles of mixing and cleaning. Also the spray pattern seems to be a little better than some of the other types on the market and it has more fill material than the other types I've used including the hobby paints.

One final note, remember that poly-urethanes (any rust preventive type of paint) and enamels (most auto spray can paints) are NOT sandable. You can sand lacquers, which are not fuel proof. Epoxies are very hard to sand because the surface is so hard. Color coat/clear coat auto paints are designed to be sanded and polished to a very high gloss ( i.e. show cars). The longer the drying time, the longer the surface flow which results in a higher gloss. By nature, Rustoleum has a very long cure time and therefore a better gloss than spray can auto enamels. If you want a fast drying paint job, use an automotive enamel. If your not in a hurry, a poly-urethane will give a little better gloss. But poly is heavy and you have to watch for runs. What you spray is what you got with poly or enamel because it cannot be sanded.