Tool Steel Drill Rod O1 is an oil-hardened, general purpose tool steel that holds its size and shape with excellent accuracy when being heat treated. While not as strong or wear resistant as A2 or D2, it experiences significantly less distortion during the heat-treating process. O1 tool steel has deep hardening properties and fine grain structure with unusual toughness. Tool steel drill rod is ground and polished to a surface finish of 16 Ra and 100% free of decarburization.