Randy,
I usually use 16 strand for 50 lb. bows. I don't like strings any heavier then necessary for performance reasons.I have tried using different thicknesses of serving material plus serving the string where the arrow/nock will be located, first with dental floss, then finally with reg. serving material. Now I just tweak the nock after dipping nock in hot water til it fits the string then I dip the nock in cool water to "set it".
God bless you. Our prayers are with you. Have a joyous Hoiday season.
Larry