However, some have an additional inside raised-area (three-line type), which can be considered as a device for prolonged use for 'ringing' although they were not designed to ring a sound any more.
また、すでに鳴らす事を放棄した設計であるにも関わらず、長期間「鳴らす」銅鐸の「延命」の工夫であるはずの内面突帯が増加（三重化）された物もある。