Observer (A-head bracket)To properly mount the Hamax Observer front position child bike seat to a threadless headset handlebar stem (or a stem with less than 2 in clearance), you will need this A head Bracket. This bracket option requires only 1 2 in of clearance on the stem and allows easy installation of the Observer seat. Installation of the A Head Bracket requires removal replacement of the handlebars by a trained bike technician. At this time, the optional Windshield