What you see is what you get
Let's have a look at the HSe-221. It has a shrink ratio of 2:1 which means it will half in size. It's rated at a size of 8.8mm, but what does that actually mean?
When flat, the tubing is 8.8mm in width. To work out the diameter of the tube when round, you need to times it by two and that will give you the circumference. Then divide that number by pi. Width of tubing while flat: 8.8mm Circumference of tubing while round: 8.8 x 2 = 17.6mm Diameter of tubing while round: 17.6 ÷ pi = 5.6mm Diameter at a 2:1 shrink ratio after shrinking: 5.6 ÷ 2 = 2.8mm So if you have a HSe-221 cassette, this tubing will be suitable for a cables with a cross-section of 2.8mm to 5.6mm. Below is a calculator to help you find the best size tubing and not just for the Brother tapes. Enter the flat width and the shrink ratio to get the diameter of the tubing before and after shrinking. A cable with a cross section between these two numbers will be suitable with that tubing size. Alternatively, click the "Change to cable diameter" link to enter the cable size instead, which will give you the approximate size of the flat tubing required.