In order to widen the field of application of a stretcher-leveler having a minimum nominal width, at least one gripping head of the stretcher-leveler is connected to an adapter having clamping elements for clamping a plate to be stretched, the adapter having a nominal width that is smaller than the minimum nominal width of the stretcher-leveler, and a plate being stretched is connected to the gripping head via the adapter clamping elements and the adapter, before starting the stretching process.