Woodwork - I have wood block of 50 * 50 * 50 mm. I want to make 1mm hole ( depth), having diameter?

The hole is only 5 mm from the edge of the wood, so there is a strong possibility of tearing the grain there. I suggest you chuck the block in a lathe and score the diameter with a razor blade, and then use a sharp chisel to excavate the inside. You probably would want a very hard wood.

I have little experience, so I am guessing at this.