You can use stainless steel gate hinges for these type of gates. Shop through a wide selection of Gate Hinges at Amazon. A basic guideline for buying a gate hinge would be a gate door that is 5 feet high, 3 feet wide and 55 pounds would be considered an average size door, while one that is 6 feet high, 4 feet wide and pounds would be considered heavy. These types of hinges for gates are also known as self-closing hinges. As far as the number of hinges you need it does depend on the type of hinge as well as the size.