Shelves about right for books (7)
I believe the answer is:
ledgers
'books' is the definition.
('ledger' can be a synonym of 'book')
'shelves about right for' is the wordplay.
'shelves' becomes 'ledges' ('ledge' can be a synonym of 'shelf').
'about' is an insertion indicator.
'right for' becomes 'r' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'ledges' enclosing 'r' is 'LEDGERS'.
Can you help me to learn more?
(Other definitions for ledgers that I've seen before include "Books listing commercial transactions" , "Account books" , "old spreadsheets" , "Books of accounts" , "Account-books" .)