Some people have used those external striped bolt head removers on Allen Head bolts. I do not know why they would work on them as they are supposed to be made for remove regular bolts with heads that have been rounded off.
But, some people have used them to remove Allen Heady type bolts.
I have seen them at Sears, Harbor Freight and Home Depot (made by Irwin). Some have more tools in their sets than others.

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84 300D, 82 Volvo 244Gl Diesel