Eight Inch Bolt is a 21 centimeter high bolt-shaped puzzle. The object is to remove the ring from the bolt. Because of pins and grooves, the ring can only slide up and down, it cannot turn. Hidden inside the ring, there is a smaller ring with a pin that runs in the maze grooves. By moving the big ring up and down, the hidden right turns sideways, pushed by the grooves. When the maze is solved by moving the ring up and down many times in a delicate sequence, it comes off at the top.
The model on the photos was 3D-printed by George Miller in 2004. This first prototype has a red top, as George ran out of black ABS wire midway his print. George also added a ruler, which indicates the solution.
Another copy of this puzzle is on permanent display at the Kinsey Institute in Bloomington, Indiana.