The Porelon Okidata Microline 420/421 Black Nylon Replacement Printer Ribbon replaces manufactures part #42377801. This ribbon provides vivid and consistent black color in addition to exceptional light fastness and durable impressions. This product has been designed and manufactured to operate the original equipment identified. 1 pack. Porelon specializes in creating inking products and elastomers for a wide variety of industries. They focus their scientific, engineering and customer service efforts on delivering solutions that perform to your exact specifications.