Oil Galley Plug Removal

What is the best tool to remove these square holes oil galley plugs? Anyone use a piece of square bar and if so what size? I do not have anything handy in this size around the garage or tool box and do not want to risk stripping. I can see someone used something non-square in one of them and it looks a little iffy.

I will replace these after cleaning with Allen key plugs.

thanks