Produced for the German army in 1933 and then became a successful commercial item. It would turn a standard 9mm or 7.65mm Luger into an inexpensive-to-shoot .22 rimfire. Unit consists of barrel insert, breech-block and toggle unit, with its own lightened recoil spring and .22 magazine. Unit was furnished with a wooden box. There were many different sized units to fit various caliber and barrel-length Lugers, but all used the same parts and concept. These units have become desirable to Luger collectors.