High Performance Air Filter for the Savage 21! Made to fit the Nitro Star 21BB engine and any engine with a 15mm wide carb neck, this is the ultimate high-flow air filter for the Savage 21 monster truck. It features a thick pre-oiled foam outer element, thin nylon mesh and another internal pre-oiled foam elements for maximum protection while allowing as much air as possible into the engine. Two nylon tie wraps are included for attaching the air filter to the carburetor.