Top 5cm Hole Bottom 3.8cm Coarse (SAE) Male Thread Length 21cm Diameter 15cm SQ FT 100 Darlly 60403 Unicel CH-942 PleatCo PWW100(Bottom) This is the Bottom filter for the piggy back filter set, you need to also buy 1 x SC736 to make up 1 set. If you have twin sets you need to purchase 2 of each type
