1.5 x 18 is the thread. A metric thread chase file, usually in stock at most auto supply stores should be enough to clean up the worst threads. If you have never used one mash up a spare bolt and practice a bit before doing the axle thread. It's patience and slow going that will get the job done best. hint use the threads on the good part to slowly work your way through the mashed up threads. Uh just so I heard, I uh have never mashed a thread myself, you see???