If Irwin can’t help, I doubt someone will know from memory.
You either need a tap/die set in m12 and then line up the different pitches to figure it out. Or if you don’t have a set, hope someone on here does and the same bender.
I’ve got the set, just not the bender.
I’d just order a nut for each pitch, there’s not many. Most common in m12 is coarse thread - 1.75 and fine thread - 1.25.
However, you can get 1.0, 1.5, 2.0 etc.
If you can’t test, find a thread that goes into the nut you have and then line it up with the bender thread. If you know your nut pitch, then you’ll know if you should go coarser or finer.
Or just order one of each I’ve listed.