The Eheim 1250 is 1/2" and 3/4" (
www.eheim.com ). The confusion comes as Danger Den likes to sell silicon hose in smaller sizes to be "stretched" onto these fittings (for the average joe with a 3/8" system). For you run the 1/2" outlet unmoded, and get a 5/8" to 1/2" conversion for the inlet and "stretch" it over the 3/4" (it's silicon, it fairly stretchable).