The Undercoating/Rustproofing UCPro Gun builds up pressure inside the tank. This pressure allows for the spraying of thicker products and assures that the rust proofing product is atomized at the tip of the wand to provide total coverage inside the cavity. The gun is recommended for both solvent based and waterborne coatings. This metal gun was built for industrial use by body shops, car dealerships and undercoating professionals yet it can easily be used by any hobbyist or do-it-yourselfer. The gun is assembled with the undercoating spray cap attached. It can be easily changed to spray cavity wax by changing this spray cap to the quick coupler and attaching the spray nozzle or wand. The rustproofing wand is 5 ft long, and comes with a hand held wand attachment and a mist wand attachment, for hard to reach areas. Also included, is the BS39 undercoating wand, spray undercoating only. Please note that some bed liners/floor coatings contain silica or rubber particles to prevent sliding. These coatings can not be sprayed with the Pro Gun. The Rustproofing wand included with the Pro Gun are for lighter coatings, i.e., cavity waxes and protective oils and can not be used to spray under coatings.