Heavy-Duty Plastic Stuffing Tubes are slightly tapered, long lasting and easy to clean.  Measures 3 9/16" at the base with a 5/16" lip.   
Use 3/8" tube to stuff sheep casings and 19-26MM collagen casings or the 3/4" tube for hog casings for 32mm collagen.  Use the 1" tube for filling meat bags or fibrous casings.