A tetrahedral chain is a particular sort of deltahedron that can be formed step-by-step, incrementally adding a single regular tetrahedron face-to-face at each step, and always adding the new tetrahedron at one of the three most recently added triangular faces. Notice that there is only one shape for three tetrahedra attached together face-to-face: the tritetrahedron or boat polyhedron. That shape can indeed be can be made by chaining tetrahedra, but the chaining process will differ according to which of three triangular faces at the stern of the boat is considered to have been the origin. In the space curve diagrams here, each tetrahedron is represented by a 70.53-degree circular arc---the dihedral angle of a tetrahedron---at the beginning of which a discrete twist of {-120, 0, +120} degrees occurs, depending on which of the three candidate faces is chosen for the attachment. The interest here is in periodic patterns in {-, 0, +} so the exact start and finish are of little consequence.
According to Adam Tyc a tetrahedral chain is at most 3-cursal, and a bit more than half are expected to be unicursal.
