Tim, yes the one with the collar is the one with the threaded plug. The plug is made from a piece of horn and the collar was carved from the horn. This horn also has a name and date on it also, think its 1828. I think you seen it at a show Tim.
The bottom horn actually is my daughters. She had the high bid in the silent auction at the CLA several years back. It has a date too I believe with really nice engraving of ships around the base.