I need help identifying a tool

Hi gang,

I have torn down my 340 and have just five more bolts to remove in the block before it goes out for hot tanking and magnafluxing and hopefully machining.
The bolts I speak of have a square indent. What is the name of the tool and where can I get one? It looks like an Allen tool fitting but square. There are three of them on the back of the block, one in the oil filter plate and one inside on the back of the passenger side cylinders. I have seen a lot of tools in my time but never have I been stumped like this before. I ask the pros for help. Thanks,

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