Four Piece Tetrahedron

Four pieces assemble into a tetrahedron.  This puzzle is not difficult but you may be confused if you are used to cube puzzles! This puzzle was invented by Wayne Daniel.

Print two copies of each piece.  The pieces do not require supports if oriented correctly.  The assembled puzzle fits in a 3" cube.

This is one of the example files in BurrTools, the stl files were generated by BurrTools with UnitSize=19 mm, Bevel=0.5 mm, offset 0.1 mm.