The Lenox Tools 20302BT318S T-Shank Bi-Metal Medium Metal Jig Saw Blade 3-5/8-Inch x 3/8-Inch x 18 TPI - 2 Pack is designed for cutting through medium gauge metal. The 18 TPI provide you with an efficient cut while giving you a smooth finish. 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.