Keypad hard

16-Button Numeric Keypad Matrix 

Rubber-domes beneath eachbutton provide satisfying key travel with each button press. Each key isemblazoned with a legible white character molded into its surface.
Fourmounting holes allow solid and easy mounting to a panel. The single-row0.1-inch-pitch solder pads are breadboard friendly. Only eight of the tensolder pads carry signals - the solder pads on the ends of the row are purelyfor mechanical attachment. The keys are connected in a 4x4 matrixconfiguration.

The overall dimensions of the keypad are 68.6mm tall(including the pcb header extension on the bottom) x 66mm wide. It will fitinto a 60mm x 60mm square cutout in a panel. The mounting holes located ineach corner are 61mm apart.
This is a great way to experiment withmatrix decoding on the Arduino!