gritnummers

Gritnummers, literally “grit numbers” in Dutch, refer to a system for classifying the coarseness of abrasive grains used in grinding, sanding and polishing. A gritnummer indicates the average particle size of the abrasive material and thereby influences material removal and the quality of the finished surface. In general, smaller grit numbers denote coarser abrasives that remove material quickly and leave a rough finish, while larger numbers denote finer abrasives that produce smoother results. Common ranges include coarse grits such as 40 to 60, medium grits such as 80 to 120, and fine grits such as 200 to 400, with very fine and micro finishes extending well above 600.

The gritnummer system is not universal; two major families of standards are the European FEPA system, which uses grit names prefixed by the letter P (for example P80, P120), and various American and Japanese schemes. FEPA sizes are intended to map to specific particle size ranges, though exact equivalents can vary by manufacturer. Abrasives labeled with gritnummers are used on papers, discs, belts, and wheels and typically come with tolerance ranges.

In practice, the choice of gritnummer depends on the task: rough shaping, deburring, and stock removal use coarser grits, while finishing and polishing use progressively finer grits. The system helps users select compatible tools and achieve repeatable results, though actual performance also depends on bonding, hardness, and grain type.

See also abrasion, sandpaper, FEPA standards, ANSI B7.1, grinding.