A machine with a fast change tool system comprises a platen (2) having fixed thereon guide means (13, 14) and a stop which provide for exact positioning of a back plate provided on an interchangeable tool. The back plate is secured to the platen by clamp members (15) each of which has a number of indexable positions corresponding to different thicknesses of back plate. The clamp members (15) are mounted on carriers (19) which are sliding fits within pockets (20) provided on the pads (9) which define the guide means (13, 14). The carriers (19) may be reversed to define alternative guide means to accomodate a relatively narrow back plate.
