7 sizes in one drill bit set (3mm, 4mm, 5mm, 6mm, 7mm, 8mm, 10mm), which perfectly meets your different needs. Specially designed for socket countersinks or pilot holes. By loosening and tightening the grub screw with a wrench (included), the countersink depth and drilling depth can be easily adjusted for screws of different lengths. The drilling length can be adjusted for different screw lengths simply loosen and tighten the grub screws. 5-flute chamfer can discharge the wood faster when drilling, with smooth countersink drilled at once to save your time and labor. The surface of the workpiece will be perfectly recessed with a screw cap. Compatible with drills with chuck, for drilling on hardwood or parquet. It is recommended to use the center punch for position before drilling, keep the drill bit vertical to avoid the drill bit bending or breaking.