Reply To: Adding spaces to large figures ? with GREP?

AFIK (Away From InDesign Keyboard) at the moment, but you can try this:

\d(?=(\d\d\d)+(?!\d))

instead of Masood’s \d(?=(\d\d\d)+\D)

In essence, it means the same — a digit followed by 3 digits followed by NOT a digit — but there is an essential difference. “\D” is “a character which is not a digit”, but “(?!\d)” means “not a digit”. That last one is also true if *nothing* follows :-)