A silencer for a firearm has a substantially cylindrical external housing with an attachment part, an intermediate part with a number of elements, and an outer muzzle part. The silencer can be releasably connected to an attachment element mounted on the barrel of a firearm. The silencer's attachment part is provided with a number of cut-outs round its circumference. The cut-outs are composed of a first portion extending longitudinally and a second portion extending over the circumference of the attachment part. The two portions are connected by an intermediate portion. In the first portion, at least one of the cut-outs will be provided with at least one bead and at least one slot is provided adjacent to the first portion extending over the circumference of the attachment part.