I needed this to finish my pepper mill. The extension cord is high quality, durable and solid. Works perfectly, without stuttering. The shank is a 3/8" hex. The internal size of the bit holder is 3/8" with two allen screws (3mm wrench not included). Both round and hex bits will work in it, but will hold hex shank bits probably better and require less torque on the screws to hold in place.The bit holder is 3/4" OD, tip to tip 5". Depending on how deep it is inserted into the chuck, it can be 1 1/2". be shorter.