The top punches for die-sets with hide-away punches are always locked in place thanks to the use of magnetic plates. These are available in several sizes and differ according to the technology with which the magnetic field is generated: electric coils constantly powered for the electro-magnetic plates (PEM) or permanent magnets for the permanent magnet plates (PMP). The PEM are the traditional solution selected over the years but recently they are being gradually replaced by the PMP due to the capacity of the latter to guarantee better performance in holding the punches in a locked position under any operating conditions and due to the improved energy efficiency. The PMP require external energy only during magnetizing and de-magnetizing stages while, during the work process, no power supply is required.