An improved tool for locking a band clamp, and an improved lock for a band clamp is disclosed. The tool includes a knife body having a knife edge that progressively cuts the free end of the band over a period of time, rather than simultaneously cutting the entire band width. In one embodiment, this is accomplished with a knife edge that is non-linear. The tool further includes a punch with a rounded or hemispherical shaped leading tip that forms an improved locking dimple. The locking dimple forms an improved lock having side walls that are, at least in part, parallel with the walls of the surrounding aperture in the band. By varying the profile of the knife edge, the punch can more fully form an improved locking dimple.