I have a knurled nut wrench, which I purchased to remove the knurled nut on
my KWM-380. It was a high quality driver. However, no matter how hard I
tried, I could not remove the nut. There simply was not enough contact. I
finally had to use a pair of pliers and destroyed the knurled nut.

That led me to not want to reassemble the switch using the same technique.
I ended up using a nice 12 sided nut. It looks fine, though not original.

So, my KWM-380 is now non-standard. That does not bother me too much since
I also have non-standard boards inside.

Colin K7FM