The best synthetic nuts out there are the ones supplied by Klann Organ
Supply, Waynesboro, Va.  The catalog nos. are HN 1, 2, 3, and 4.  They,
and another type of synthetic nut are shown on this Klann webpage:

  http://www.klannorgan.com/pdf/miscellaneous.pdf

They never snap the wires, take thread impression readily, and can be
turned with a nut driver.  They have an excellent dome on the contact
surface and do not appear to harden over time.

Jim McFarland