Vision Metron 4D Flat M.A.S. Handlebar w/extensions31.8x420mm 290mm J-Bend. The Vision Metron 4D Flat M.A.S. Handlebar is designed for aerodynamic efficiency and ergonomic comfort in road triathlon and time trial disciplines. Its unique 4D shaping promotes a natural wrist angle while the integrated Modular Aero System (M.A.S.) allows for fine-tuned positioning. This handlebar is ideal for riders seeking a streamlined cockpit with enhanced control and reduced fatigue over long distances.