Triumph Twist Drill 71603 5/16-24 NF T66HDSET High Speed Steel Taper, Plug and Bottom Tap Thundertap Bronze Oxide Coated Tap Set with Taper tap 7-10 lead in threads, Plug tap with 3-5 lead in threads, Bottom tap with 1-2 lead in threads High Speed Steel Bronze oxide Recommended drill size is letter I for 75 percent of theoretical threads Made in the USA