14 minutes ago, wiilydog said:

you can also trying hammering a smaller six sided socket on to the bolt if you are struggling to find a replacement key.

6 into 10 hardened steel could be difficult.

On 09/09/2020 at 17:21, MicMac said:

6 into 10 hardened steel could be difficult.

Also the ridges are on the inside of the bolt head, leaving the outside smooth and round, IIRC. You can get impact sockets for this sort of thing for air/electric impact tools. Try Machine Mart for starters and then check online for similar cheaper stuff.