I'd like to be able to use them as manifolded doubles as well but now I need to take apart my tanks and measure the valves because I'm not sure if I have 3/4 or 7/8 I know it sure looks skinny but I'm not going to swear to either because of the flange around the base of the valve and I can't actually see the threaded opening and haven't since my last hydro. 3 years ago.