Foam Prefilter for Mag-Drive Models: 250 GPH, 350 GPH, 500 GPH, 700 GPH and Hydro-Air 1200 Pumps. 

Also alternatively available; Compact Rigid Prefilter Item# 12785 and Rigid Prefilter Item# 12784

approx:

3 1/4" H x 4 1/2" W x 5 1/2" L