In a compressible unit a plurality of separating discs are provided and adapted to being capable, in a compressed state, of being mounted in and removed from a centrifugal separator rotor, which rotor during operation is rotatable about an axis of rotation. The unit includes a support, a pressure surface, between which the separating discs are disposed abutting against one another. Guide surfaces abut against the separating discs and control radial and polar position. At least one compression mechanism is adapted during compression of the unit to press the support and pressure surface towards one another so that the discs are compressed. During compression, the guide surfaces allow relative movement between the support and pressure surface and the separating discs, and are of at least sufficient extent in the compression direction for the position-controlling abutment between the guide surfaces and the separating discs to be maintained throughout the relative movement during the compression.