White ceramic knobs (Central Crouch End N8)

3cm W x 2cm D. Not sure what size screw/bolt they need.
10 in very good condition, 8 with small chips in collar: see photo, with the chipped ones in front (sadly dropped on hard tiles this week!) Depending on the angle they're viewed from, the chips might not be noticeable. Just found another two slightly chipped ones, so there are 20 altogether.