A hinge has a pin, a rotating positioning element and a stationary positioning element. The rotating positioning element is mounted around the pin and has a first, second, third and fourth detent and a rear surface with an inner circular area and an outer circular area. The first and second detents are formed in the inner circular area. The third and fourth detents are formed in the outer circular area. Each detent has a centerline. The centerlines of the first and third detents coincide. The centerlines of the second and fourth detents coincide. The stationary positioning element is mounted around the pin and has a first protrusion and a second protrusion. The first protrusion is formed on the stationary positioning element and selectively engages the first and second detents. The second protrusion is formed on the stationary positioning element and selectively engages the third and fourth detents.