Atoplee 1/4" Hex Shank HSS Titanium Coated 4-22mm Step Drill Bit for Carbon Steel This is HSS High Speed Steel Step Drill/Pagoda Drill Bit With the Titanium coated to reduce friction and heat. Suit for use in hardness under 25  artifacts,The plate thickness under 5 mm. Cannot be used for stainless steel Shaft Type: Hex Shank; Surface treatment: Ti