I use the one with 1 1/2 inner diameter. From mcmaster, you can choose inner and outer diameters, width, material, plus various models that attatch in different ways (one piece, two piece, "clamp on", double collars, etc). Just check their site and try to measure your sack where the shaft collar will go.
Limitations start when you start choosing the options. For example, if you start by choosing the 1 1/4 inner diameter, you can´t choose 2 1/2 outer diameter or some material or whatever. I say this to explain how it works, not sure if the example is accurate, but you will see when you check their catalog.