The IBM Model M4-1 Space Saver Numeric Keypad was the complimentary numeric keyboard option available for pairing with Model M4-1 keyboards. It features the same assembly design as the Model M3 numeric keypad, however, the case is enlarged to match the design of the host keyboard and various layout variations exist - most commonly, an extra "00" key is added at the expense of reducing the "0/Ins" key to a single key-unit size. Without modification, these keypads can only be used when coupled to an M4-1 (or M4) host keyboard via a modular 10P10C ("RJ-50"-like) cable. The only real difference between this M4-1 version and the M4 version is purely the sticker on the back.