The mechanism installed by Ben Katin at the edge of the Kiyor: a wheel that lowers the basin into its well every evening, “so that its water not be disqualified by the night.” The Gemara names only the wheel (Yoma 37a); the well comes from Rashi. The tour gives it a post, a crossbeam, a strut, a spoked wheel and a chain reaching to the edge of the basin.
Sources
Project decisionTour's choice: the shape of the mechanism. The sources give only two features: a wheel (Yoma 37a) and wood, whose sound could be heard (Tamid 1:4). Post, crossbeam and chain are designed for the tour; no source mentions a chain.