Carbon steel grades 12L14, 1215, 1144, and 1117 are formulated to ensure the best machining qualities. They're best for parts that don't require welding, such as shaft couplings and mandrels.

Stronger and harder than carbon steel, alloy steel is preferred for high-stress applications, such as axles, torsion bars, and drive shafts. It includes alloys 4130, 4140, 4340, ES2100, and 8620.