There are several different Fluid Film formula's. Fluid Film "NAS" is the most popular formula. "NAS" is used for all undercoating, general lubrication, and rust preventing applications. When Fluid Film "NAS" is packaged in aerosol cans, it becomes Fluid Film "AS". So if you have used Fluid Film in the spray can, and want it in bulk (gallons, pails, etc), you would buy the Fluid Film "NAS" products.
Fluid Film "Liquid A" is a thinner, marine formula for interior applications,(rudder interiors, voids, etc.) Not recommended for vehicle undercoating.
Fluid Film "AR" is a very thick semi-gel for heavy marine applications. Not recommended for vehicle undercoating.
Note: Fluid Film NAS is the recommended product for vehicle undercoat.