Abstract: A method and apparatus for mounting a die, particularly a rigid cutting die, on a die cylinder includes having a bubble along a seal on the die to bridge any gaps between the die and the die cylinder when the die is initially positioned on the die cylinder. This bubble seal enables a vacuum to be applied between the initially positioned die and the die cylinder to pull the die down against and into conformity with the surface of the die cylinder, at the same time flattening the bubble seal. A key at a trailing edge of the die locates in an axial keyway in the die cylinder to circumferentially position the die; a bolt is then inserted at a leading edge of the die to establish axial location. During operation the die is held in position by the vacuum. Beam sensors and light reflectors may be incorporated to sense when a wrong die is present and shut down the apparatus.