MilesCraft 1390 Drill 90. Solid Steel Drive for long lasting durability. Ergonomic handle provides firm comfortable grip. Reversible for left or right hand use. Fits all 3/8 inch and larger drills. Includes Chuck and Key. Note: Best results with this attachment are achieved with corded power drills at 1000 rpm or faster with twist and spade drill bits 1 1/4 inch and smaller. NOT intended for use with: Any drill bit larger than 1 1/4 inch, hole saw cutters (any size), or auger style bits (any size)