This normalizing is followed by tempering to make the material stronger. Certified heat-treats the parts in large furnaces using multiple rows of electrical conduit, similar to a giant toaster. Their facility can normalize and heat-treat material as small as nuts and bolts and as big as complete chassis or giant structures for cranes and airplanes. Plus they can help strengthen both mild steel and exotic alloy components. In the end the substructures had a hardness rating of 34 to 38 Rockwell, which is similar to a Grade 8 bolt.