Naming the Hexacube pieces — Page 3 of 5

Group 2 — continued (crosssection of 5 units) Where the addition of a sixth cubelet makes a piece fit into either of two shapes by crosssection — in this case, L or Y — we've given priority to Y. The L family gets only those pieces that cannot look like a Y but only like an L. By a quirk of symmetry, piece Y3 is congruent to Yb3, so the Y family has only 9 members (there is no Yb3).
The drawing shows the numbering key of the cube faces, front and back, and the attached cube as a smaller square in its respective position. The 3D views show each piece from an angle so all 6 cubes are identifiable.

