Countersink Drill Bit Set Including - Each countersink is made from heat treated tool steel for durable and repeatable performance with easily replaceable HSS (High Speed Steel) drill bits, including #5/#6/#8/#10/#12 head diameter and hex shank. Quick Change - Standard 1/4 inch hex shank is quick change compatible and has an adjustable counter sleeve depth with Allen wrench.The bits have self-starting point and five-fluted design eliminates chatter and vibration for smooth operation to make clean, accurate and burr-free cuts. Unique Designed - Unique designed steel countersinking and counterboring pilot hole to allow a suitably sized plug to be fitted over the screw-head; Secured with hex wrench for easy replacement and adjustment.Perfect for plastic,wood and metal,perfect for home DIY and general building/engineering use. Easy To Use - Adjustable counter sleeve depth with hex wrench,drilling length can be adjusted for various length screws simply by loosening and tightening the setscrew,Suitable for most types of hand drills. Widely Use - Great for wood openings, reaming, chamfering, screw head and so on.Suitable for wooden planks, plywood, aluminum board, fiberboard, particle board, plastic, PVC board and other various soft material chamfer.