Cost-effective set,1pcs 7 inch forstner bit extension (5-3/4" Drilling depth) +1pcs 10 inch forstner bit extension (8-3/4" Drilling depth) +2pcs hex spanner key, with 2pcs chuck wrench key (10+13mm). Helps reaching awkward, difficult corners in your projects Round shank support forstner bits with shank diameter of 3/8" or slightly smaller. Compatible with shank types drill bit extension includes two fixed screws and hexagonal spanner. To secure the shank in place, tighten these screws with the hexagonal spanner, easy to use. During the operation, the drill chuck can be tightened with a drill chuck wrench to further enhance work efficiency The traditional forstner drill extensions were prone to slipping when working with hardwoods, so we developed a non-slip design for the part that attaches to the drill rig, so that the drill jaws can firmly grip the extension extension bit set are built with rugged,high carbon steel for structural stability,with ground and polished surfaces; The shanks are 3/8" in diameter and fit most drills Voltage: 18 Color: As Shown Material: Metal Package Contents: 1*set drill bit extension Only the above package content, other products are not included. Note: Light reflection and different displays may cause the color of the item in the picture a little different from the real thing. The measurement allowed error is +/- 1-3cm.