\:d\:b+\:d

That is a digit followed by 0 or more whitespace characters followed by a digit

However if you want to use

([0-9\+\.\-]+)(\:b+)([0-9\+\.\-]+)?

That will match any group of at least one numbers, periods and plus or minus signs followed by any number of at least 1 whitespace followed again by any number of at least one number, period plus minus even none at all. However it would also match +-..9

However, I think you really mean more like this:

([\-\+]?[0-9]+(?:[\.]?+[0-9]+)?)\:b+

This means 0 or 1 of either a plus or minus sign, followed by at least 1 but as many as necessary digits, followed by 0 or 1 of period and at least 1 number ... that defines a number as long as you don't want comas.

Then

^((\:b*)(([\-\+]?[0-9]+([\.]?+[0-9]+)?)(\:b*)))+$

Matches a whole line. Starting with any number of white spaces followed by a number (like above) and any number of white space... the whole thing repeated over and over as many times as necessary.

Does that help?

As I read your message again I see it doesn't ... here is the replacement:

Search for this:

([\-\+]?[0-9]+(?:[\.]?+[0-9]+)?)(\:b+)([\-\+]?[0-9]+(?:[\.]?+[0-9]+)?)(\:b+)?

Replace with this:

\1 \3

Set Unix Regex on.