Nearly all screwheads are circular (with the exception of squareheaded coachscrews); I'm afraid your description doesn't help identify it.
If there is a pin in the centre, it's likely that it is a security screw and you may be able to undo it with one of these.
However, security bits are so widely available nowadays that some manufacturers have had to adopt special designs, the tools for which are sold only to accredited users.
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