Thyristors conduct AC (alternating current) in one direction or one half of an AC cycle. A TRIAC (triode AC) conducts current in either direction when its gate is triggered. Other names include bidirectional triode thyristor or bilateral triode thyristor. TRIAC types are snubberless, alternistor, internally triggered, logic gate and standard which are chassis, surface or through-hole mount. Selection is by off state voltage, on state current, hold current and gate trigger voltage.