Yanmar Ignition Switch Question

[Buttercup]

Hello, This is an odd question, but here it goes. My Yanmar ignition switch and key assembly is held into place by a cheap plastic knurled ring. The plastic ring broke about a year ago. I used J B Weld to glue it back together, and it held for a year. Now it broke again and I just want to replace the ring, but you can't get the ring without buying the entire ignition assembly.

I tried buying a nut of the same size at the hardware store, but apparently the threads are not the same and I couldn't fully engage the nut on the switch.

I also don't want to replace the ignition switch with a generic automotive switch.

I has anybody experienced this, and how did you fix it??

Thanks,
Steve