Square Hole Drill Bit Set: come with 1 square hole bit adapter and 4 square hole drill bits, for bench drill and hand drill clamp diameters ranging from 38 to 55 mm/ 1.5 to 2.2 inches for easy installation and use; Please note that it is only suitable for bench drill and hand drill with clamps Quality Materials: the square hole drill bit adapter is made of quality steel, strong and , can firmly fix the wood, drill machine mounting diameter of different mortise accessories, cutting is precision machined, reduce the use of error, specially designed with mortise bit accessories drill bit will not be blocked by wood chips, high hardness, no rolling, cutting speed, the bit is , please take it out safely Efficient and Accurate: the bit adapter and the matching drill attachments in 4 sizes easier to use, and the precision design of the drill press mortise attachment ensures that you can drill the right mortise and mortise holes in the fastest way; More convenient and faster than mortise