Narex Twist Gimlet 3 Piece Set with 3, 4 and 5 mm Sizes for Screw Sizes #4 through #8. Made by a small tool manufacturer in the Czech Republic The set comes with 3 sizes, 3, 4 and 5 mm and will make tapered pilot holes for screws #4 through #8 Blades have threaded tips with machined spiral flutes Blades made from unbreakable forged and hardened steel.