dennishoddy It depends on what type of casing you are using, if you are using cellulose casings then you probably will need to either tie them or use hogs rings, tying them would be my suggestion there. If you are using natural casings like sheep or hogs then you shouldn’t need to use anything at all, they should stay twisted once done. If you are using collagen casings then you can twist them but once you cut them they casing will come open a little, you could tie these if you want but I generally don’t, as long as collagen casings are cooked at the correct temperature they should expand too much past the casing.
For a good example of how to twist casings go to the 4:35 mark of this video https://www.youtube.com/watch?v=q_FgktFx4Xg Austin is twisting cellulose casings here but it shows how to twist.
Let us know if you need anything else!