In an attempt to solve starting probs detailed elsewhere, I would like to remove my starter. It seems to be held on with just bolts into the flywheel housing (is that what it's called? The engine bit anyway!) The head of the bolts looks like this...

An 8mm Allen key is too small, and a 10mm won't go in. However with that shape I'm not convinced an Allen key is right. It looks like a 12 pointed thing would go in. Can someone who has done this on a JX point me in the right direction? From what I've read, petrols use bolt-and-nut, but I see no nut on the engine side of things...
Thanks in advance

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