by Guest » Wed Aug 10, 2005 3:43 am
English bolts are threads per inch. The pitch, or inches per thread is the inverse of that.
Metric is millimeters per thread.
Since 1" = 25.4 mm, if you divide 25.4 by the threads per inch, you'll get the pitch in mm.
As an example, a 1/4-20 bolt has a 25.4/20 = 1.27 mm thread pitch (which would not be a standard metric thread). Standard metric bolts and screws have well defined rules for diameter and thread pitch.