It was first discovered by Day and coworkers in 2002 as an inclusion complex containing CB[5] by fractional crystallization of the cucurbituril reaction mixture.[7] The CB[10]•CB[5] was unambiguously identified by single crystal X-ray structural analysis that revealed the complex resembled a molecular gyroscope. In this case, the free rotation of the CB[5] within the CB[10] cavity mimics the independent rotation of a flywheel within the frame of a gyroscope.