Wera 3840/1 TS 4.0mm hex insert bit for 1/4" hex drive is designed to keep rust at bay. Wera's Stainless tool line is manufactured from 100% Stainless steel, preventing extraneous rust caused by use of conventional tools contaminating stainless fasteners. Wera's unique vacuum ice-hardened process gives the necessary hardness for industrial applications. Torsion (TZ) bits are designed to prevent premature wear for improved service life. Hex-Plus technology prevents rounding of screw recess and transfers up to 20% more torque. Stainless bits partnered with Wera's stainless Rapidaptor will protect the full length of the bit against extraneous rust. Ice-blue design features make the stainless tools easy to identify. German engineered. Bit dimensions: 1/4” hex drive; 4.0mm hex x 1”. Wera – The Best Tools For The Job!