[cypher]

Which species is he?
Sometimes with russian dwarfs the nails grow long whatever you try to give them to keep them trim & it can be hard even for a vet to trim them sometimes! If you can't do it yourself then best to ask the vet though.
Someone suggested using a small box, a terry's chocolate orange box in their case, that the hamster might like to dig in with a small piece of sandpaper in the bottom, maybe a little sand on top of that then you could scatter a little substrate & a few seeds to encourage digging in there, might only work for a dwarf though & I haven't tried it myself.
I wouldn't recommend using sandpaper any other way btw as it can hurt their feet if they're on it too long.