Your Rheem equipment has a factory model number and serial number on a sticker-like label or metallic tag attached to the unit in a place away from moving parts (usually near the handle, under the seat, or on the side of the unit). The best way to buy repair parts for your Rheem is to begin by searching for your Rheem model number on PartsTree and use the OEM Rheem parts diagrams to find the parts that fit exactly like the originals from the Rheem factory. When you locate your Rheem model tag, take a picture for future repair parts needs.
To buy engine parts for your Rheem, like an air filter, oil filter, fuel filter, spark plug, tune-up kit, or carburetor parts, you will likely need to search separately on PartsTree for your engine model. On Rheem equipment, the engine model and specification ("spec") numbers, as well as serial number and sometimes type and code, are often stamped above the muffler, by the spark plug, or near the overhead valve cover.