The Xcelite 99PS41MM 9-Piece Allen Hex Socket Screwdriver Set (Metric Sizes) features compact interchangeable blades designed for recessed 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.