There's a single nylon gear. The rest are made of metal. They've been using a sacrificial worm gear since the 1960s. KitchenAid switched to all-metal gears on

There's a single nylon gear. The rest are made of metal. They've been using a sacrificial worm gear since the 1960s. KitchenAid switched to all-metal gears on their high-end models fairly recently. In the past, all models had a nylon gear, but the new high-end mixers use electronics to protect the motor.