The Model M15 numeric keypad was an optional accompaniment for the Model M15 adjustable keyboard. It takes the form of a 17-key buckling springs keypad based on Model M1/M2 design principles like its host keyboard and uses a proprietary modular connection. The keypad also has four flip-out feet to allow the user to match the profile of the host keyboard and its adjustable ergonomic feet. These are most likely the smallest official IBM buckling springs device available.