The K&N Replacement Air Filters for the UMP Off-Road Air Box: part 55-1000 has a 3 inch outlet and part 55-1001 has a 4 inch outlet. These air filters were designed to achieve high, virtually unrestricted airflow while maintaining filtration levels critical to your engine.
K&N Off-Road Air Filter Kit (UMP Airbox w/ 4in Opening) Air Cleaner Assembly