Replacement Briggs & Stratton Air Filter. Fits Briggs & Stratton 3.5 HP Original Quantum Series 100700 Engine. Air Filter Dimensions: 4-5/8" x 4-5/8" x 7/8" Item: BAF-115, 399877, bs-399877 O.E. Replacement Part Number: 399877 , 399877S , 5028 , 30-720 , 100-420 , 102-541 , B1SB2841 , 2841 Features Fits Briggs & Stratton 3.5 HP original Quantum series 100700 engine Replaces OE # 399877 Contains one air filter