Don't let a long day at the crag mess with the integrity of your belaying. With the Mammut Smart 2. 0 Belay Device, you'll have the help of assisted braking on your side. This lightweight belay device is perfect for gym and sport climbing, especially on long days spend climbing and lowering at the crag. Built to handle ropes between 8. 7 and 10. 5 millimeters wide, the Smart works well with any HMS locking carabiner and lowers smoothly and securely even when you're a little beat up from the day.