I only use 3 size tubing on the Moe's Grinder: 4", 1 1/2" and 1 1/4" all in 11 gauge. Yeah, I know, 1 1/4 won't fit inside 1 1/2" 11 gauge. I mill a grove to match the internal weld of the 1 1/2" and get a good fit with some extra thickness for threading.