When I had my single post RB300 this one works very well with the stock nut on the P3 table.http://www.expressimoaudio.com/Index/100_5491.jpg
It is thin and fit in the P3 hole I had perfect. If anything it needed to be widened very little to turn it easily. Sand paper would do, no grinding etc.
It fits from the top of the hole and secured with the original nut.
Expressimo also sells the extended nut.
Pathos Classic One MKII, Clearaudio Emotion CMB Carbon Satisfy Arm, Usher CP6371, iFi Phono, Cinmag stepup, ATOC9/ML II, Dyna 10X5, Marantz SA15 S2 Ltd., all "Silver Series" WyWires.