The shaft passer is a device which was invented by the ancient Greeks. Hero, for instance, built a mechanical horse which could have a sword passed through its neck without decapitating it. It is basically a wheel with a wide thin rim, scalloped deeply in 3 symmetrical locations to produce a shape which looks a little like the object on the flag of the Isle of Man (UK). The axle of the wheel is set within one assembly and the rim of the rest of the wheel is held in a suitable groove in the other part of the assembly. If an object (shaft) passes between the 2 assemblies, they remain linked at some point (due to the flanged wheel) throughout the process, but the shaft nevertheless passes, like a pedestrian through a turnstile. The device tends to jam easily. A concerted attempt was made to avoid this problem about 25 years ago by making it out of Teflon, and thus provide a safetly line for boats which did not have to be unhitched when passing stanchions. It met with limited success.