The following is information from one of the persons who helped with the design of the bell.
It was made by the Amish Kraft Co, Grabill, IN. They start with a solid brass rod that is fed into a lathe that makes the bell. There is a small cavity in which an O-ring or grommet is inserted. The clapper is made so that it can be pushed up past the O-ring into a cavity that was made to receive it.
The Amish are a religious group that do not believe in using modern conveniences such as plumbing, electricity & telephones. This particular family-run business uses a diesel generator in their manufacturing facility to power the machinery, thus they do not need to depend on public utilities.
Many thanks for finding the information about the clapper on this bell. We have copied your findings and will be sending it, along with our latest newsletter about our weekend in Cambridge, to all BCBI members.