It is a 50 amp connection. The three prongs are the two hotlegs and the neutral connectors. The forth connection is the ground connection that is the shiny metal connection that is on the side of the plug that mates with the connector on the inside of the receptacle.
https://www.amazon.com/ParkPower-636...zcF9hdGY&psc=1
https://www.amazon.com/Shopcorp-50A-...1&sr=8-42&th=1