From Ephinea PSO Wiki
- Raises the attack value of equipped weapons by 1.
No effect if a weapon is already upgraded to the maximum limit.
Monogrinder is an uncommon item used to add 1 grind to a weapon. Monogrinder can be used by selecting the "Use" option with a weapon equipped. If the equipped weapon is already at its maximum grind value, Monogrinder can't be used.