Hexastix
Hexastix is a symmetric arrangement of non-intersecting prisms, that when extended infinitely, fill exactly 3/4 of space. The prisms in a hexastix arrangement are all parallel to 4 directions on the body-centered cubic lattice. In The Symmetries of Things, John Horton Conway, Heidi Burgiel, and Chaim Goodman-Strauss named this structure hexastix. (Wikipedia).
