A spectacle blind is an item used in pipelines to either block or allow the flow of fluid by rotating it. It consists of two metal discs connected by a central web, resembling a pair of spectacles: one disc is a solid plate (the blind) for complete shut-off, and the other is an open ring (the spacer) to permit flow. This design allows for quick isolation and re-pressurization of a pipe section for maintenance or testing by simply rotating the device instead of removing it, unlike a standard blind flange.