One of the quality features on my urns is that I make wood finials to seal the urn vessel opening. I cut threads into the wood so that the finial screws on to the top of the urn body making a tight fit that does not require any sealant. I put together a pair of videos to help demonstrate this technique and I hope that it is a useful resource for anyone wanting to learn how to thread chase. Feel free to reach out if you have any questions.
Video Part 1
Video Part 2