Water Heater Pressure Relief Valve Outlet Size?

SidecarFlip wrote:
It's a standard box store / hardware store T&P valve just like you have on your residential HWH. One size basically fits all.

Well that's why I asked. I'm going through my handy Grainger catalog here and I'm seeing valves with an outlet size of 1/2, 3/4, 1 and even larger. I'm not seeing much consistency.

I think I'm just going to take 3/8, 1/2 and 3/4 fittings to be safe.