Hold on, don't try to re-tap it just yet as you might do more harm than good.
There are actually 3 variations of the M9 thread, these are 9 x 1.25 metric course thread and 9 x 0.75, and 9 x 1 metric fine threads.
There are also a number of other thread variants that come very close to what you describe.UNC, UNF, BSF and BSW could all figure in this.
I would suggest you investigate more, unless what you intend to re-tap has little value to you.
