Steel 4142-Prehardened Square Bar 3/16" square Retail Price

About 4142|Chromium-molybdenum alloy steel with 0.42% carbon. Sits right between 4140 (0.40% C) and 4145 (0.45% C). In practice, most machinists can't tell it apart from 4140 at the lathe. Same heat treatment response, same machinability, same applications. Often shows up when a distributor stocks material that falls in the overlap between 4140 and 4145 specs. Compare to 4140 (functionally identical for most purposes) and 4150 (higher carbon, higher hardness capability).

About Square Bar|Solid square stock used for keys, keystock, spacers, and parts with flat reference surfaces. It's easier to clamp in a vise than round bar when you need to mill features on multiple sides.