Atoplee Titanium Coated HSS Step Drill Bit 6-25mm,1/4 inch Hex Shank This is HSS High Speed Steel Step Drill/Pagoda Drill Bit With the Titanium coated to reduce fric 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