It is missing its centercap first off. With that and absent the collar, its pretty normal unless the not provided dimensions are different from standard. So, presumably the question has more to do with the collar. It doesn't appear to be a bushing for a bigger opening unless there is a threaded portion below the collar which has sheered off. I have seen a lot of bushings to adapt one type of fuse to a different opening or to allow the insertion of case shot.
Was it recovered from a Civil War era location? Shortly, I will be posting some post war Schenkl fuses, some with war era dates and some with dates well past the end of hostilities. This was a highly effective fuse and continued to be used for 3+ decades after the war ended.
