OEM Husqvarna air filter cover kit which includes the air filter, air filter cover, knob and bolt. The part number for the air filter is 537186301. The part number for the cover is 503888001. The part number for the knob is 502204001. This kit will fit the Husqvarna trimmer models 123C, 123L, 123LD, 223L, 223R, 322L, 323C, 323E, 323HE3, 323L, 323LD, 323P4, 323R, 323RJ, 325C, 325CX, 325EX, 325HDA55, 325HDA65, 325HE3X, 325HE4X, 325L, 325LDX, 325LX, 325P4X, 325P5X, 325RDX, 325RJX and 325RX.