What is it? Looks like a Torx bolt but it's not

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Working on our TT, trying to remove the Air Flow Sensor as it's misbehaving. However, 2 bolts have got me baffled. They look to have a star-shaped recess like a Torx socket. However, there is also a lump in the centre of the recess meaning a Torx socket will not fit. Anyone have an idea what I need?

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Thanks guys - this is a nice shiney Audi TT though, not a shed. I don't think the girlfriend would like me to set to it with a hammer ;-)

I'll take the car to Halfords and see which fits - thanks, I now know what to ask for.

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Yeah, whatever happened to a good old 1/2 inch nut & bolt? I only needed 2 sizes to dismantyle my Mk1 Escort - 1/2 and 9/16.