If you have lost or have a damaged pulley nut, I have a kit consisting of a 20mm ID special nut and tabbed locking washer. Don’t be fooled by cheap china knockoffs, These are OEM USA made parts.
If the threads are damaged on your cartridge, then I suggest that you send the cartridge to me for repair. I install new nuts as needed and at no extra cost when I rebuild the cartridge. I will also repair damaged threads at no extra cost as well.