Interlocking - Three-Piece Block

Three-Piece Block (Stewart Coffin)
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Three-Piece Block (Tom Lensch)
Designer:Stewart Coffin
Craftsman:Stewart Coffin (1st)
Tom Lensch (2nd))

Ten cubic blocks are joined by half or quarter of one face to make three pieces. The puzzle has threefold axial symmetry. Unbelievably difficult puzzle considering there are only three pieces. Stewart made 350 from 1980 to 1983. Number 38 in his numbering system.
Three-Piece Block - Pieces

More information in The Puzzling World of Polyhedral Dissections