Can someone measure the threads on the chassis ground point that is between the 2 bolts holes for the rear left light cluster?

I've tried an M5 but it doesn't seem to fit and binds up tight before full insertion. It is a new panel (with a thread boss included) and has been painted so it may just need threads cleaned, but I'm worried that it may not be an standard M5 and retapping with the wrong pitch may ruin it. I have to borrow this tap and need to know the pitch.