Rat nails

Question
Is there a specific type of stone or brick that you would recommend to put in our cage to help wear our pet rats nails down.

Answer
I would use a regular nail file.  I dont like putting things like that in the cage. Should the rat fall on it, it could cause serious injuries, including head trauma. Iknow of a rat that fell from a shelf and hit her head on a brick left in the bottom of the cage for their nails.  She was OK, thankfully, but it could have been a disaster.  Filing their nails gently, going in one direction, or using a finger nail clipper and just taking the tip off is much safer.  The older the rats get the less sharp their nails are due wearing down as they age.