I must admit that this is the first time I see something like this and it looks like a home-made invention to me. The lens is protected from the edge of the sleeve by a fiber pad, but it is not attached in any way and simply falls out of the housing. It looks like someone tried to glue it with some cement - to no avail. It is hard to believe that the manufacturer anticipated the need to manipulate something like this in night observation conditions.
On the other hand, I'm wondering about the thread. I don't know what the sleeve is made of - but if it is galvanized brass, then making the thread yourself would result in exposing the original metal...