The Milwaukee Thin Kerf 4 in. Metal Cutting Sawzall Blades with the Double Duty Upgrade have an optimized tooth form for the longest life and increased speed. These metal Sawzall blades provide the strongest blade tang on the market with Tough Neck ribs. The deep stamped rib design is engineered to protect against tang breakage. The 4-inch saw blade has a short and thin-profile with 24 TPI making them ideal for fast, flexible cuts.