They are pressure plate sensors to replace step pads and buttons. Good for thousands of presses. Durable. Have had 600lbs of players on 1 single board. 
 
Comes fully assembled with 2qty 12" leads to connect
 
Full is 4" x 2 3/4" x 1/4" high fully assembled
 
Half is 2" x 2"3/4" x 1/4" high fully assembled