Two types of Leas one is is a heavy-duty cushion web lead Specialized 24 ft recall lead in British made quality material and the other is a similar length but lighter weight nylon recall lead normally used for smaller dogs. These leads are the classic way to teach recall, it is far better if you use a whistle in conjunction with this technique.
This should be an acme whistle (see my products). It carries further and stronger than the human voice.
More importantly, it is far more commanding and does not sound emotional and panicky. which the human voice can impart.