a punch face 28 the punch face has a circular cutting perimeter 29 with a diameter smaller than the diameter of the passage so it can act as a punch with a shearing action the punch face is slanted or mitered so as to present two cutting edges 30 31 which extend from a forward extreme to the edge of a dihedral 32 persons familiar with punch dies will recognize these shapes and the punch die art is directly applicable to this punch piston an attenuator 35 is an elastomeric ring placed between the wall of the cylinder and the punch piston 39 s shank it will snub the movement of the punch piston after the bolt has been freed a rigid insert 40 in the cavity of the body forms a transmission chamber 41 which enlarges from a smaller diameter to the diameter of the head of the punch piston a body 42 of liquid or liquifiable material is placed in the transmission chamber by this term is meant a substance which is or can be made sufficiently plastic or deformable as to receive and transmit a force behaving as a fluid while doing so for higher pressure usages this may be a body of lead which becomes plastic in the sense of deformation under sufficient pressure alternatively it could be a body of silicone rubber or even a true liquid if loss of liquid can adequately be prevented in all cases the pressure applied to it is transmitted as such an amplification cylinder 50 is located concentrically next to the insert it houses a differential piston 51 with a large head 52 slideably fitted in cylinder 50 its rod 53 has a lesser diameter and fits closely in.