Your Ryobi 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 Ryobi is to begin by searching for your Ryobi model number on PartsTree and use the OEM Ryobi parts diagrams to find the parts that fit exactly like the originals from the Ryobi factory. When you locate your Ryobi model tag, take a picture for future repair parts needs.
To buy engine parts for your Ryobi, 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 Ryobi 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.