I only found this website today while trying to identify scrap waveguide components during a shed clearout. This item, see https://www.flickr.com/photos/161663409@N03/44239680852/in/dateposted-public/ seems relevant to the discussion but my question is "what metal is the shiny lustrous block on the sliding rod inside the waveguide?" Its S.G. seems to be about 8.2 Many thanks.
A second photo is at https://www.flickr.com/photos/161663409@N03/42479828220/in/dateposted-public/