Description:

16-Button Numeric Keypad Matrix 

Rubber-domes beneath each button provide satisfying key travel with each button press. Each key is emblazoned with a legible white character molded into its surface.
Four mounting holes allow solid and easy mounting to a panel. The single-row 0.1-inch-pitch solder pads are breadboard friendly. Only eight of the ten solder pads carry signals - the solder pads on the ends of the row are purely for mechanical attachment. The keys are connected in a 4x4 matrix configuration.

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

Documents:

• Datasheet