The set comprises all three sizes: 3, 4 and 5mm screws (gauges 6, 8 and 10). Projects such as decking, fencing and flooring often involve driving a large number of screws. If the task also involves drilling a pilot hole and countersink then the Turbo Bit could save you time and effort. Designed for speed, this combined drill and countersink is both fast and accurate. It has a 1/4" hex shank for use in a chuck or holder. The shank is hardened aluminium so not suitable for a magnetic bit holder. The bit is stainless steel and operates much like a flat bit, which is how it gets its speed. A rotating stop collar prevents the bit from marking the surrounding surface. The drilling depth including countersink is 30mm, suitable for screws 30mm to 40mm long.