Grit

         Grit refers to the size of abrasives. However, due to the irregular shape of most abrasives, international standards employ different mesh sieves to extract abrasives within a certain range of sizes and consider them as the same grit size. Since mesh sieves are used, let's explain the numbering system for mesh sieves: The standard for mesh sieves is based on the number of openings per inch (25.4mm). For example, if there are 60 openings per inch, it is referred to as 60 mesh, written as 60 Mesh, or referred to as a #60 sieve.
        Upon closer examination, the aperture of a mesh sieve can be calculated using the formula: (25.4mm/mesh size) - wire diameter. However, what we are primarily concerned about is the aperture size. Therefore, the American Society for Testing and Materials (ASTM) has established a reference table correlating mesh sizes with aperture sizes. The following table provides reference values for commonly used mesh sizes.

             There are three main standards for specifying abrasive grain sizes: ANSI, FEPA, and JIS. Let's focus on the most common standard, which is the FEPA standard. FEPA stands for the Federation of European Producers of Abrasives.
FEPA defines several standards:

• F: Applicable to bonded abrasives, such as ceramic or resin-bonded grinding wheels.
• P: Applicable to coated abrasives, such as sandpaper or abrasive cloth.
• D: Applicable to diamond abrasives.
• B: Applicable to CBN abrasives.

         I'll provide an explanation of the FEPA standard focusing on the most commonly used F standard. In the FEPA standard, a given grit size of abrasive does not have a uniform particle size but rather follows a Gaussian distribution of particle sizes. Taking F80 as an example, the average particle size is 180μm. FEPA specifies that particles larger than 212μm should not exceed 3% of the total, and particles larger than 150μm should constitute more than 94% of the total.
Using this logic, let's interpret the following FEPA standards:

         For finer grit sizes like F220, which falls into the category of micro powders, there are separate specifications for particle sizes. For materials like CBN or diamond micro powders, the particle sizes are often described using a range. For example, 10-20μm indicates that the majority of the abrasive particles fall between 10μm and 20μm, with at least 95% of the particles being larger than 10μm, and a maximum of 5% being larger than 20μm.

          I would also like to provide a commonly used quick calculation formula. Divide 15000μm by the grit size, and you will get an approximate value for the average particle size of that grit. For example, for F60 abrasive, 15000μm/60 = 250μm.