The Unibit® step drill bit features as single radial concave flute design for smooth, even cutting and virtually round holes. Ideal for drilling holes in steel, copper, brass, aluminum and other thin materials. 1/4" shanks; self-starting. Hardened industrial grade high-speed steel 4-piece set includes: #1 Bit drills 13 holes: 1/8" to 1/2" in 1/8" steps; #2 Bit drills 6 holes: 13/16" to 1/2" in 1/16" steps; #3 Bit drills 9 holes: 1/4" to 3/4" in 1/16" steps; #1 bit with Titanium Nitride Coating.