26 mm Beryllium Dome Tweeter4 ohm, Neo, Small Chamber, Grill- 1" Beryllium Diaphragm (99% pure Be)- Patented Symmetrical Drive (SD-2) motor- Die Cast Housing & Face Plate- Large Roll Surround f. wide dispersion- Compact Non Resonant Alu Rear Champer- Sound Transparant Protective Grill LINK: Beryllium Safety Data Sheet