The Lenox Tools 20305BT406S T-Shank Bi-Metal Wood Cutting Jig Saw Blade 4-Inch x 3/8-Inch x 6 TPI - 2 Pack is designed for fast rough cuts in wood. The 6 TPI allow you to cut extremely quickly, while the sharpness of the carbon steel and the precision ground teeth give you a smooth cut. The teeth are ground to precision sharpness for straight cuts. The Bi-Metal Construction makes the blade more durable and flexible than a traditional Carbon Steel Blade. These blades are made specifically for jig saws that take T-Shanks.