The wera 3950 spkl9 sm metric hex key set with keys made from high grade stainless steel are vacuum ice hardened for industrial strength made from round bar with machined ends for a precision fit and extra strength the use of stainless tools with stainless steel fasteners prevents the cross contamination of metal preventing rust from a galvanic process traditional hexagon socket screws can be easily rounded by the sharp edges of the tool pressing against the inside of the screw profile the hex p