Shimano SL-BS79 Outer Cable Guide to hold outer cables straight, preventing any kinks or narrowing which could affect breaking performance. Shimano recommends the use of these SL-BS79 outer cable guides when you are running outer cables under bar tape (ie higher end STI levers or bar end shifters/brakes). They hold the outer cable straight and prevent the bar tape causing any kinks or narrowing of the outer, which could affect shifting/braking performance. It is also useful for bars without cable grooves, as they help to retain the free cable movement but are also comfortable when under the bar tape.