Piezoelectric sounders. Ceramic buzzer element. 85db min (15vp-p, 4khz square wave, 10cm). Capacitance at 1khz: 10000pf. Max input voltage 30 vp-p. Enclosed black plastic case 24.4mm round with 2 mount tabs 29.3mm centers and 2 wire leads 2-3/4". Marked RC24C.