Some of the links on this forum allow SMF, at no cost to you, to earn a small commission when you click through and make a purchase. Let me know if you have any questions about this.
Casing size determines the tube needed, but either would probably work. As long as you can hold your hand around the casing to control the casing flow onto the meat coming out of the tube it should work. One closer to the proper size would probably work better (less tendency for meat to back up on the outside of the tube towards the roll of casings and your hand), but it should be manageable in a pinch.