CMXZDCG478 8 ft Chain Rail Extension Kit Buy Now CMXZDCG478 8 ft Chain Rail Extension Kit Buy Now The 8 ft. Chain Rail Extension Kit is used to complete garage door opener installations on chain drive garages with up to 8 ft. garage doors. Add to Wishlist Features HEIGHT EXTENSION: Allows your chain drive garage door to handle up to 8 ft. doors Includes (1) CMXZDCG478 Steel Rail Extension with Replacement Chain (1) Set of Required Hardware Support No Limited Warranty Unfortunately, this specific product is not eligible for any warranty. Whilst this product is not eligible, further information about our warranties can be located below. Learn More Service We take extensive measures to ensure all our products are made to the very highest standards and meet all relevant regulations. Learn More Manuals CRAFTSMAN manuals are available to help put your tools in operation.