With a +/- 0.020 tolerance over the entire surface, some will need lapping for razor use. I'm not the only fella' to find it necessary to do. I haven't heard what the design criteria was re. lapping.

I'll be among the first to say that they are absolutely miserable to lap. While lapping them in my bathroom (water for the DMT), at one point, I actually considered installing a cable-TV connection in there.