It can sometimes be necessary to trim your rats toe nails but instead of trying to hold him and do it with clippers, you can get things like Lava Ledges or bricks and put in their cage. When they run, jump, and climb on these things, it trims their nails down automatically.
I have these Lava Ledges in both rat cages and all my boys climb on them which helps to keep their nails trimmed. They also chew on it which is good for their teeth.
You can get a brick and put it under the water bottle so that when they go to get a drink they step on it and that will help trim their nails.