Pro tharsis xc stemthe tharsis xc stem is the next evolution of headset design featuring a unique pinch bolt design with a headset preload ring the tharsis xc allows the headset to be adjusted without the need for a top cap leaving the fork steerer tube free to take an internal di2 battery or simply as a method to save weight featuresunique pinch bolt design with headset preload ring enable the headset to be adjusted without the need for a top cap or star nut leaving the fork steerer tube free