Brand New Worm Drive / Pinion Gear Assembly is an original KitchenAid stand mixer replacement part. The worm drive is made of nylon and is designed to strip away to prevent further motor damage when there is a failure. Installation may require the application of new Gearbox Grease (part # 4176597). Check for model compatibility before purchasing. Brand New Worm Drive / Pinion Gear is an original KitchenAid stand mixer replacement part. Made of nylon & is designed to strip away to prevent further motor damage when there is a failure. Installation may require the application of new Gearbox Grease (part # 4176597).