Our two metal resonator bars are clearly marked D and A. The bars are mounted on durable plastic sound boxes with built-in legs, which makes them easy to hold and play OR to place on a flat surface for playing. When the rubber mallet (two 7 1/2" mallets included) strikes the center of a bar, a clear ringing tone is produced. Bars are 6" x 1 1/4" x 1 /4" and safety rated for 3 years+.