Manufacturers vary in how they number pricking irons, stitching chisels, pricking wheels, overstitch wheels, and other stitch line marking tools for different stitch densities.
Stitches Per Unit Length
Many English and American manufacturers number by stitches per inch. This is particularly common for overstitch wheels.
Traditional French toolmakers, such as Vergez Blanchard, mark by the number of stitches per Paris inch.
Distance Between Points
Some number in millimeters or fractional inches between the points of the tines.
Distance Between Tines
Some number in millimeters or fractional inches between the leading edge of each tine to the tailing edge of the next.
Teeth Per Unit Length
Traditional Japanese toolmakers mark their irons by the number of teeth per sun (寸).