The terms Mesh and Grit are often misunderstood and confused. When it comes to discussing these terms in regard to abrasive blasting or similar, the terms are used interchangeably. A 60 mesh Aluminum Oxide can also correctly be termed a 60 grit Aluminum Oxide.
The differences arise when trying to determine the exact particle size of a 60 grit (or mesh) product. Each of the terms would be more correctly defined as follows:
Mesh is a count of the number of evenly spaced openings in one square inch of a screen (i.e., screen size). Mesh is basically a specific size or dimension (see Mesh and Micron).
Grit is generally defined as an angular media used to abrade or cut a work piece. Grit is a specified range of particles for a given product.
In practical terms, identifying a specific abrasive product with the term 60 Mesh would normally indicate that the product has an median size of the openings on a 60 mesh screen. The term 60 Grit more accurately identifies the particle size distribution of the product.
Take a quick look at this specifications sheet for 60 Mesh Aluminum Oxide Grit. The Screen Size is the Mesh and the overall Particle Size Distribution is the Grit.
Whether calling an abrasive product Mesh or Grit ultimately makes no practical difference.