Shimano ST-4S20 is a Rapidfire Plus shifter designed for use with 7-speed drivetrains. It features a lightweight design with a polymer body and a forged aluminum lever for durability.

The ST-4S20's Rapidfire Plus shifting mechanism allows for quick and precise gear changes with minimal effort. The shifter can be operated with either the thumb or index finger, and its ergonomic design provides a comfortable grip.

The ST-4S20 also features an optical gear display that provides a visual indication of the current gear position. This makes it easy to see which gear you're in, even when riding in low-light conditions.