These pieces are a scale-accurate representation of the peptide backbone of a protein.

See this video for a demonstration: https://www.youtube.com/watch?v=1usemtIYe_s&lc=z22sgljh3qywe5kkyacdp43apn3hcrnjte0qxqfcvulw03c010c&feature=em-comments

Most of the angles are fixed (as they are in an actual protein), but connecting the pieces with 1/8" set screws allows the user to simulate rotation about the phi and psi dihedral angles to make secondary structures like beta sheets and alpha helices.

Note: These are the set screws that I use to connect the pieces: Alloy Steel Set Screw, Black Oxide Finish, Hex Socket Drive, Meets ASME B18.3/ASTM F912, 1/2" Length, #6-32 UNC Threads, Imported (Pack of 100) https://www.amazon.com/gp/product/B000FN3WUC/ref=oh_aui_detailpage_o00_s00?ie=UTF8&psc=1