land rover series 3 seatbelt bolt size

I've just taken out the bolts behind front seat for seatbelt to be renewed, they go into the floor and seem to screw into a bolt welded onto the underside , however I have cross threaded one , What size are they M10 bots are too small and M12s are too big , should I just knock bolt off from underside and use new bolt and but , it sounds easier but would bolt come off ?

Thanks

7/16th unf