Drillpro 3 Piece HSS Titanium Step Drill Bits Set Metric Sizes Bits HSS Metric Spiral Flute Step Drill Bit 4-12mm, 4-20mm, 3-12mm For drilling holes in thin material such as steel, stainless steel, copper, aluminum, or plastic Titanium Coated Material: HSS steel Two-flute design for faster, smoother cutting