Extension Tap, Thread Size #4-40, UNC, Overall Length 4", HSS-E, Black Oxide, Right Hand

The black-oxide finish on these taps retains lubricants to improve the taps' wear resistance and chip flow. Black-oxide taps should only be used on ferrous metals. High-performance taps are harder and more wear-resistant than high-speed steel taps. They provide good precision and accuracy in threading tasks. Spiral-point taps have straight flutes with a spiral point that pushes chips in front of the tap as it moves into a hole and out the other side, eventually forcing the chips out of the hole. They are used for threading through holes.