No need for you to insert hardwood or ply inserts in your stabs or fins for brace wire attachment points.

          During construction, in a convenient location of hard balsa, drill a 1/8” hole, then insert and CA a piece of 1/8” o.d. aluminum tubing. The tubing is easily sanded flush to the surface.

          When ready, attach the brace wire fittings using a 2-56 bolt which fits the tube perfectly. If your stab or fin is thicker than 3/4”, use 2-56 threaded rod cut to size with a nut on both ends.