A 1/4" or 5/16" socket (Can't remember which one), fits my brake adjusters. I've also got a special brake adjuster spanner. I'll post a photo the morn. Kinda dark, cold, and wet out there just now
1978 LHD SAAB 96 1978 MGB Roadster 2008 LHD "Classic" Renault Twingo 1991 Nissan Figaro
You need a 5/16" square brake spanner (or socket), which can be had from eBay or a motor factors for less than a fiver. An open 5/16" or 8mm spanner will work too, unless the adjuster is badly stuck.