Well seals consist of two round disks which sandwich a flexible rubber donut in between. The lower disk is threaded so that when the screws on top are tightened, the disks come together and expand the rubber out against the inside wall of the casing. This locks the seal like a plug inside any standard 2" ID well casing.
The EarthStraw well seal is made from structurally reinforced ABS and comes with the EarthStraw gripper in the center.
My old 4" well casing had collapsed about 20 feet down at water level where it rusted out years ago. I pounded down 42 feet to rock a new 2" pipe inside. Then I covered and cemented over the old casing leaving the 2" pipe extending out. The 2" well seal fit and tightened well to the pipe. It could have gripped the straw gripper tighter but it does hold it satisfactorily while pumping . It seals the pipe from allowing anything from falling into it as well. The whole system works well and I would recommend it.