White ceramic knobs (Central Crouch End N8)

3cm W x 2cm D. Not sure what size screw/bolt they need.
21 altogether (photo shows 19). 11 are in very good condition, 9 have small chips in the collar, and one has a slightly larger chip. Photo shows all but a couple of them, with the ones with small chips in front (sadly dropped on hard tiles this week!) Depending on the angle they're viewed from (i.e. seen from above or below), the chips might not be noticeable.