Stainless steel anti-loose screws 1.6mm galvanized steel enclosure, gray powder coated, dustproof, moisture-proof 20 watt amplifier single or five party lines for intercommunication dual color led for power-on and off-hook overload protection with current limiting and thermal shutdown circuits modular pcb fuse protection for power supply and speaker amplifier surge protection for power supply sealing magnet switch equipped in the hook dynamic microphone for noise cancelling and feedback preventing available for 110vac or 220vac adjustable speaker volume from the front panel mute setting of speaker equipped with power supply and speaker amplifier ulcul listed, class l, division 2, class ii, division 2, class iii, nema 12 cns certified, ex nc iic t6 ex td a22 t5085â°c, ip54 cqst certified, ex nacl iic t6 gc dip a22 ta t6, ip54 k25ag0 - indoor five party wall mount handset station k21ag0 - indoor single party wall mount handset station.