3D-Trominoes

Connecting three squares edge to edge at 90 or 180 degree angles you can get 11 different pieces with a total of 33 squares. You can use these pieces to construct a 3x3x1 open dispaly case or typesetting box. Furthermore you can swap bottom squares and missing squares at the top to get various puzzle problems. It's possible to print nine pieces without support but two ones need a support. The open box can stabilize the constructions. Set of pieces with more squares are called polyominoids. (OEIS A056846)