Zandstra says about the Separate 3M Polishing Strip Per Set From 3 Pieces
For an optimal sharpening result there are 6 different grades of
self-adhesive lapp film on a specially extruded aluminium triangle.
The length of the triangle is 25 cms.
The micro aluminium oxide gives the edge a very shiny surface.
The aluminium triangle comes complete with 3 different polishing strips. 3 Grades are standard glued to the triangle. Namely 40 (blue), 30
(green) and 3(pink) Micron. 2 Additional grades are available. 9 (light
blue) and 12 (yellow) Micron.