About 52100|The bearing steel. 1% carbon, 1.5% chromium. This is what ball bearings and roller bearings are made from. Heat treats to HRC 60-64 with exceptional wear resistance and fatigue life when properly processed. In the annealed condition (spheroidized) it machines well with carbide tooling. After hardening, it's grinding and honing only. Also popular in the knifemaking world for its fine grain and excellent edge retention. Compare to 440C stainless (similar hardness with corrosion resistance) and M2 HSS tool steel (even harder but overkill for bearing applications).
About Round Bar|The default starting stock for lathe work. It gets turned, bored, and parted into shafts, pins, bushings, spacers, and just about anything round.
