The National Hockey League (NHL) is a professional ice hockey league composed of 32 teams, founded in 1917. Each team may select a captain, who has the "privilege of discussing with the referee any questions relating to interpretation of rules which may arise during the progress of a game." Each team is also permitted to select alternate captains, who serve when the captain is not on the ice. Captains are required to wear the letter "C" on their uniform for identification while alternate captains wear the letter "A"; both letters are 3 inches (7.6 cm) in height.