How are these constructed? Are they 3 piece with a rubber washer that expands when the bolt is tightened? I plan on making my own, but I have not seen one in person to undrestand the constuction. Ive seen pics showing two rubber seals.
(http://i4.photobucket.com/albums/y126/hundredpercentkill/dmf/IMG00046-20100711-1248.jpg)