EDITED BY CHARLES BATES
SENIOR EDITOR

An easy way to convert metric surface call outs to standard U.S. ones (rms) is to mentally multiply the metric value by 40. For example, 1.6 = 63 rms, 3.2 = 125 rms, and 6.3 = 250 rms. And for metric "triangle" callouts you can approximate one triangle = 250 finish, two triangles = 125 finish, and three triangles = 32 to 63 finish. But for a quick reference, the conversion chart available from Grindwell Norton Ltd.(www.grindwellnorton.co.in/grindingtech/pdfs/surfacefinish.pdf) below helps.

Danny Van Deusen
Haddam, Conn.