FSA OS-99 CSI Stem

The hybrid design combines the high structural stiffness of a 3D-forged aluminum core with the vibration-damping characteristics of a carbon fiber wrap. This results in a stem that feels responsive and rigid during sprints while helping to smooth out road buzz for a more comfortable ride.

The OS-99 CSI is compatible with both 1-1/8-inch and 1-1/4-inch steerer tubes, making it a versatile option for a wide range of modern road and gravel bikes.

This stem is designed for standard 31.8mm diameter handlebars, which is the most common size for modern performance road and mountain bike cockpits.

The OS-99 CSI weighs 126 grams. The use of titanium hardware and a sculpted faceplate helps keep this weight low without sacrificing the strength needed for high-performance riding.

The stack height is 41mm. You should ensure you have enough steerer tube length or appropriate spacers to accommodate this measurement when installing it on your bike.

Yes, its combination of durability and vibration damping makes it a great choice for gravel bikes. The hybrid construction handles rougher terrain well while keeping the front end light and agile.