The Xcelite 99PS60 11-Piece Bristol Multiple-Spline Socket Screwdriver Set features compact interchangeable blades designed for Bristol multiple-spline socket head screws. The set also includes the Model 99X5 extension, which adds 4 inches in length. The model 991 Handle holds the blade shaft firmly, yet permits quick, easy insertion and removal. The blades are made from high-quality steel, hardened and tempered for optimum performance. The set is supplied with a convenient see-through stand-up plastic case.