A good size for a nanoblock might be a cube 200 nanometers …

A good size for a nanoblock might be a cube 200 nanometers on a side (the distance your fingernails grow in three minutes).
https://twetch.app/t/3bf693cc4c1bb9944aa6070c81e3de405e9a4d8750c3704a1a022a04f69f68ec