Genuine Husqvarna Air Filter Part #: 581 04 74-01 Fits Husqvarna: 325 HE3- 966787601, 325 HE4- 966787701, 525 HF3S, 525 LK, 525 P4S, 525 P5S, 525 PT5S, 525 RJX, 525 RK, 525 RXT