Saws have strong aluminum and steel frames that allow 15,000 psi (28,000 for HK1228) tension on the blades for straighter cuts and longer blade life. Both frames come with Bi-Metal blades and provide storage for extra blades. The HK1228 can hold a projecting blade as a job saw. Bi-Metal blades have a high speed steel cutting edge and are electron beam welded to alloy steel back, with wavy set. When used with high tension frames, provide best performance and safety.