I am wanting to have a building fixed for "generator ready" with an external power inlet box.

I am supposed to buy a 50 Amp Power Inlet box and was told to get a "four prong" 50 Amp generator power inlet box.

I have found 50 Amp power inlet boxes from Reliance Controls. but their picture of their various boxes all use the same pictures and I can't tell if they are 4 prong or not. Electrical supplier here says if they order me one and it's not 4 prong, I'm stuck with it.

Anyway, Reliance Controls website lists 2 kinds of 50 Amp generator power inlet boxes:

1. PB50: This says "Nema Configuration CS6375, connector required is CS6364"

2. PB51: This one says it is a CS6360 configuration. Doesn't say anything about connector required.

Which one of these do you think is indeed a 4 prong male connection?