The prescribed number of Benkan was six as it was one for each of right (U) and left (Sa) Daiben, Chuben, and Shoben, respectively, but as provisional posts were permitted up to two for each of Chuben and Shoben, it was called 'Eight Ben.'
定員は左右の大弁・中弁・少弁各1名の合計6名であるが、中弁・少弁において合計2名まで権官の設置が許されて「八弁」と称された。