A folding wing hinge for a wing having a fixed wing portion and a folding wing portion, the folding wing hinge comprising: a hinge pin including a hinge pin spline and having a first longitudinal axis; an input fitting coupled to one of the fixed wing portion and the folding wing portion, the input fitting including an input fitting spline (705, 705A) and a second longitudinal axis; and a spline coupling member configured to couple with the hinge pin spline and the input fitting spline (705, 705A) so that the first longitudinal axis is moveable relative to the second longitudinal axis by a first predetermined amount of movement; wherein the hinge pin spline is an external spline having teeth with a crowned tooth surface and the spline coupling member includes a first mating spline portion having an internal straight-sided spline configured to couple with the hinge pin spline; and wherein one of: a) the input fitting spline is an external spline having teeth with a crowned tooth surface and the spline coupling member includes a second mating spline portion having an internal straight-sided spline configured to couple with the input fitting spline, wherein the respective crowned tooth surfaces of each of the hinge pin spline and the input fitting spline form respective universal joints (1020, 1021) with the spline coupling member; and b) the input fitting spline is an internal straight-sided spline and the spline coupling member includes a second mating spline portion having teeth with a crowned tooth surface configured to couple with the input fitting spline, wherein crowned tooth surfaces of the hinge pin spline and tooth surfaces of the input fitting spline form respective universal joints (1020, 1022) with the spline coupling member. a hinge pin including a hinge pin spline and having a first longitudinal axis; an input fitting coupled to one of the fixed wing portion and the folding wing portion, the input fitting including an input fitting spline (705, 705A) and a second longitudinal axis; and a spline coupling member configured to couple with the hinge pin spline and the input fitting spline (705, 705A) so that the first longitudinal axis is moveable relative to the second longitudinal axis by a first predetermined amount of movement; wherein the hinge pin spline is an external spline having teeth with a crowned tooth surface and the spline coupling member includes a first mating spline portion having an internal straight-sided spline configured to couple with the hinge pin spline; and wherein one of: a) the input fitting spline is an external spline having teeth with a crowned tooth surface and the spline coupling member includes a second mating spline portion having an internal straight-sided spline configured to couple with the input fitting spline, wherein the respective crowned tooth surfaces of each of the hinge pin spline and the input fitting spline form respective universal joints (1020, 1021) with the spline coupling member; and b) the input fitting spline is an internal straight-sided spline and the spline coupling member includes a second mating spline portion having teeth with a crowned tooth surface configured to couple with the input fitting spline, wherein crowned tooth surfaces of the hinge pin spline and tooth surfaces of the input fitting spline form respective universal joints (1020, 1022) with the spline coupling member. a) the input fitting spline is an external spline having teeth with a crowned tooth surface and the spline coupling member includes a second mating spline portion having an internal straight-sided spline configured to couple with the input fitting spline, wherein the respective crowned tooth surfaces of each of the hinge pin spline and the input fitting spline form respective universal joints (1020, 1021) with the spline coupling member; and b) the input fitting spline is an internal straight-sided spline and the spline coupling member includes a second mating spline portion having teeth with a crowned tooth surface configured to couple with the input fitting spline, wherein crowned tooth surfaces of the hinge pin spline and tooth surfaces of the input fitting spline form respective universal joints (1020, 1022) with the spline coupling member.