Hexagonal spanner for Fidelity Research FR 66S tonearm

Elliot, In your first photo, that huge nut with two flat sides is the unique nut for the B60 base.  That's a costly option that facilitates VTA adjustment and also adds mass to the tonearm base. Without the B60 base, the nut is hexagonal and much less massive, and you adjust VTA with set screws as shown in your last photo.

Believe mine is like Elliot's, with the 2 flat sides. Am hoping to find the right tool locally.

So maybe my memory is faulty in that the huge nut with parallel flat surfaces is common to setup both with and without the B60.  But if that is the case, why would your manual refer to a "hexagonal" nut? With the B60 nut, no hexagonal wrench is appropriate.  Just grab it with an adjustable wrench, the kind with two flat surfaces that move together or apart with the spiral shaped adjuster, and Bob’s your uncle. More likely, you have the B60 VTA adjuster there, which would account for the discrepancy between the language of the manual and the nut you are looking at. The B60 adds at least $500 of value to the ensemble, IMO. Maybe more.

Here is a photo. Have not been able to remove the black knob (I assume it is supposed to be removable and is part of the B60 VTA adjustment?) Before I take a large wrench to a part of an expensive mechanism that does not belong to me, I ask for further guidance.