Wera 05059554001 851/4 BTZ 1/4'' Hex Phillips Power Drive Bit are designed for phillips screws and feature BiTorsion zone to absorb peak loads which considerably reduces the risk of breakage, greatly extending the products service life. Wera 851/4 BTZ 1/4'' Hex Phillips ® Power Drive Bits are ductile and tough for hard materials and are suitable for holders as per DIN ISO 1173-F 6.3.