Quizzled - you are actually correct ! Clue should read:
'Short, thick books for 500 in study' according to Terry's other posting in 'Crosswords' subsection. 'D' makes a difference! Well Done, ☺ja
Terry D - you've also posted this on crosswords, where you've given the full clue - including ....'books for 500' ....ie bb (books) instead of D (500) in study. !