The device in the sawbench switch is a bridge rectifier but because only 3 terminals are connected only 2 of the 4 diodes in the bridge are being used; the 2 diodes have their cathodes connected together. One of the diodes feeds the no-volt dc solenoid while the other is a protection diode connected in reverse across the solenoid.
In normal use when the green ON button is pressed this solenoid is energised; if the mains power is temporarily disconnected the solenoid will de-energise which will allow the spring in the solenoid to physically move the push buttons into the OFF position so that if power is later restored the saw will not unexpectedly start up.
Hagrid, September 2010