Performer displays a small platform holding a tri-fold screen.
At the bottom of the screen is a square transparent window. Visible through the window is the bottom portion of a clear acrylic tube. Also displayed is a yellow and a red cube. The yellow cube is held above the screen and dropped into the tube where it lands at the bottom and is visible through the window. Not much of a trick so far until the performer removes the screen. The spectator will be shocked to see that passing through clear are two bolts and nuts completely obstructing the tube. It's impossible for the solid cube to pass through.
This is a really offbeat and clever piece of magic.