Three Intersecting Tetrahedral Helices
Three helices composed of tetrahedra can intersect at a single point, where they merge into a single tetrahedron. The edges of that tetrahedron can form the bases of helices, contained within enveloping cylinders.
 Wikipedia. "Boerdijk–Coxeter Helix." (Dec 19, 2019) en.wikipedia.org/wiki/Boerdijk%E2%80%93Coxeter_helix.