MD1222 is for use with the Large 4" tank opening and the INLET and OUTLET are both 1 1/2" Threaded, and uses 1 1/2" distributor ( riser pipe ) opening ( no pipe included ).Includes distributor o-ring and top of tank o-ring. Piping connections are 1.5" standard pipe thread female.The distribution head is designed for single in-out applications on simple filters such as sediment removal, taste, odor or pH neutralization. This economical head fits onto standard 4" - 8 NPSM tank openings, and uses the 1 1/2" riser pipe ( again - NO pipe included ).