Have a look at this one TC -
https://rimmerbros.com/Item--i-FS108207L - it holds the small handbrake bracket ,#9 here
https://rimmerbros.com/Item--i-GRID001570. Its says 20mm for that one - the one I've taken off is about 18mm.
The bracket I'm talking about is quite a serious affair - about 3in long with a flange and a grommet for the hose to pass through - it must have a p/n. If it does, the screw will too.