The clear polycarbonate dust shield has two main functions. It collects debris, dust and chippings, which is particularly important when working overhead. It also acts as a guide ensuring that the drill bit is always at right angles to the work surface. The boring head passes through a large ball race bearing so runs very smoothly. Two cutters, one on each of the graduated arms gives you a balanced performance minimising vibration. The cutting depth is adjustable up to a maximum of 46mm. The ability to bore holes from 40 to 200mm diameter allows you great versatility. Use with a variable speed drill, the larger the diameter the slower the speed.