Coarse, Medium, Fine Knurls vs. TPI (Teeth per inch) Knurls
In the middle of the 20th century, some knurl manufacturers (Armstrong and Williams) sold only 3 different pitches of diagonal knurling wheels as standard: Coarse, Medium and Fine.
They measured the pitch of their tools by the “transverse TPI” (TTPI) as shown below. 1/transverse circular pitch = TTPI. The 3 pitches were:
So, for example, a 14 TTPI diagonal wheel is actually a little “finer”, not coarser, than a 16 NTPI wheel. This has caused much confusion over the years.
Except for those 3 TPI’s, Accu Trak ,and I believe all other current knurl manufacturers, produce their diagonal and diamond knurling wheels to the “normal TPI” (TPI) = 1/normal circular pitch.
Metric knurls throughout the world are produced to the “normal circular pitch” measured in millimeters (mm).
The actual number of teeth on all our stock wheels can be found under “Technical Info” at the top of our website home page. There may be a few items missed as we continually add new stock items.
There is no exact definition for course, medium and fine knurling. If that is the callout on a drawing, you have some leeway on either side of what is shown above.
Accu Trak Tool Corp.