When you wish to add a lid to a turned hollow vessel there are many ways. A lid needs to be secure if it is to hold contents like ashes in a funeral urn. The rim is often thin and not suitable to chasing threads in it. So turners glue another piece of wood to the rim before it is turned so that there is enough depth in which to turn threads. This means adding a block of wood, chasing threads in the vessel and chasing threads in the lid. If you are not careful changes in humidity can cause the threads to lock so it cannot be opened easily.
I have a bias towards doing things with economy. Above is a funeral urn I turned many years ago at the request of a relative. The wood has colored nicely with the passage of time.
Below is a photo of the rim of the hollow vessel. Notice that because the wood was turned green as it dried it shrank and it is no longer a perfect circle but is more of an oval. It is wider top and bottom and narrower side to side.
If you turn a lid to fit in the rim it will be circular and won’t fit inside the rim of the vessel. However if you turn the lid to the greatest diameter of the rim using calipers to make the measurement then the upper and lower part of the lid will fit in the rim but not the sides of the lid. Take a sander or gouge and trim the sides of the lid until the lid will fit all the way in the rim. It should fit loosely and not snugly.The lid below is slightly longer top to bottom than side to side.
When you twist the oval shaped lid inside the oval shaped rim it will bind when you twist it 5 to 20 degrees, or so, and will be quite secure. To loosen the lid you just untwist is and it will come out easily. Since there is enough play in the fit when the oval lid is inserted into the oval rim changes in humidity are never great enough to hinder removal of the lid. Yet with an easy twist the lid is very secure. To my simple mind this is ever so much easier than having to glue another piece of wood to the vessel and then chase threads in the rim and the lid. What do you think?