BAC One-Eleven silencer kit for its notoriously loud engines.
https://s3-us-west-1.amazonaws.com/h...n_silencer.jpg
Previously:
https://www.homemadetools.net/forum/...473#post151107
https://www.homemadetools.net/forum/...559#post158947
https://www.homemadetools.net/forum/...1317#post74166