Grinding of 52100 Material Grinding of 52100 Material Butchie1946 (Industrial) (OP) 24 Jun 15 17:31 I have a 52100 part Spherical Dia. on the end and here is what the drawing asks for. .2500 +/-.0002 Dia. with a another note stating Sphericity to be within .00005 on Diameter. Should this be one or the other and not both. Looking for some information on this. RE: Grinding of 52100 Material ornerynorsk (Industrial) 24 Jun 15 18:50 Diameter and sphericity are 2 different things. Sphericity is the allowable deviation from the spherical form, regardless of the diameter. It is essentially the 3 dimensional version of "roundness" It is better to have enough ideas for some of them to be wrong, than to be always right by having no ideas at all.