What do the letter/number code mean on an abrasive grinding wheel?

You may see a code on grinding discs, such as A24R on a DW4523.

First letter = abrasive material
A= Aluminum Oxide (usually metal)
S- Silicone Carbine (usually masonry)
C- Ceramic
D- Diamond
B- Cubic Boron Nitride
Z- Zirconium (metals)

Second digit(s) (number)- Grain size. Similar to sand paper grades, the lower the number, the coarser; the higher the number, the finer. Goes from 8 to 1200.

Next Letter- Wheel grade- A (soft) to Z (hard)

For instance- A24R means – Aluminum Oxide, 24 grit, about mid hardness.