Oregon 30-137 5-1/8" by 3-1/2" by 1-1/2" Lawn Mower Air Filters Oregon 30-137 Replacement Stihl Air Filter 5-1/8" L x 3-1/2" W x 1-1/2" H Fits early versions of BR320, 340, 400, 420 back pack blowers Replaces Stihl 4203-141-0301