1. An ink stick for use in a solid ink feed system of a phase change ink printer, wherein the solid ink feed system includes an elongate ink stick feed channel with an elongate shaped guide rail extending in a feed direction, and a key plate covering at least a portion of the ink stick feed channel along the feed direction, wherein the key plate has an insertion opening providing access in an insertion direction into the feed channel, the ink stick comprising: a three dimensional ink stick body having a guide surface and an insertion perimeter; and a non-planar shaped guide element formed in the guide surface shaped to interact with the elongate shaped guide rail of the solid ink feed system for guiding the ink stick along the guide rail; wherein the ink stick insertion perimeter is in a plane substantially perpendicular to the insertion direction; wherein the insertion direction is substantially different from the feed direction; and wherein the insertion perimeter has at least one perimeter section forming a nonlinear key element that matches in size and shape a nonlinear key element in the perimeter of the key plate insertion opening.