Abstract: A ball-and-stick model system representing alpha carbon positions and the peptide link between adjacent alpha carbons as modeling elements of two-piece sets. Each two-piece set comprises complementary ring rods and ball rods, the latter having a generally cylindrical body enlarged at one end to a sphere form with a slot through a portion of the enlargement. The ring rod also includes a generally cylindrical body with an enlarged end portion to fit snugly within the slot of the ball rod so that when they are fitted together they appear as a sphere with the cylindrical body portions extending outwardly therefrom. The cylindrical portions of adjacent model sets are united by a pintle and hole structure configured so that when fitted together a continuous cylindrical body extends between adjacent spheres.