i used a box spanner. then ground another down. only to find I had a thin walled deep socket ! I think any web search for a thin walled socket will provide one usable. however a single hex ( 6 point) rather than a double hex ( 12 point) is stronger.
common issue is excess torque when fitting plugs an then heat etc we get adhesion to threads with potential stripping! always use a plug thread lube when fitting . copper slip is common but nickel based is far better and now used by major engine manufactures. even on injectors! it helps prevent spalling.adhesion of threads . apply to one half of a plug ( lower section near tip NOT upper near gas seal) filling threads to full for approx 50% of circumference.
this when placing plug in cyl head the compound gets spread along thread gaps slowly upwards to wards gas seal. tighten as normal( unless ham fisted bugger then use a torque wrench ) most plugs simply need to have a 'feel' for gas seal compressing then we get a sudden 'high resistance' that os gas seal compressed fully. a half turn to max 3/4 turn normally ensures a gas safe and correctly tightened plug.
excuse excess info here . I was employed as engine tester for a well know engine maker in Dagenham on thames . so have put probably several hundred plugs into cyl heads. cast iron .alumimium and many many injectors too. after fist few years fitting and refitting plugs for engines on test . we started using anti-seize compound. copper based normally but later switched to nickel as far superior. hope my rambling is of some use to somebody !