These replacement ribbon cartridges are compatible with a variety of POS, calculator and typewriter products: The housing of each ribbon spool measures 2 inches in diameter, ribbon itself measures 1/2 inch by 24 feet. These universal typewriter ribbons replace manufacturers parts for Adler, Brother, Olivetti, Olympia, Royal, Sears, Silver Reed, Smith Corona and Swintec. This item is most popularly used for the Smith Corona models Clipper, Comet, Compact, Silent, and Standard. This product is also interchangeable with the GRC models T5-77B and the T17-77B. They produce a rich black color and are designed to work with the original equipment manufactured. Use of this product will not void the original warranty.