Since , Formula One teams have been required to build the chassis in which they compete, and consequently the distinction between the terms "team" and "constructor" became less pronounced, though engines may still be produced by a different entity. This requirement distinguishes the sport from series such as the IndyCar Series which allows teams to purchase chassis, and "spec series" such as GP2, which require all cars be kept to an identical specification. It also effectively prohibits privateers, which were common even in Formula One well into the 1970s.