Personally I don't know. I can tell you that I bought a 30-33" but I do remember having to cut it as it was too long for my little 14.2 or 3 hand Paint mare. We have had to cute my fake tail multiple times for her and place it very high because when you would back her she would rip out the fake tail. So she actually broke my loop. ): But mine still works wonderfully, I might eventually even send it in and get it fixed. Now that being said even though we cut it, my tail still looks great on my 15.1 hand paint gelding with absolutely no tail! I'm not even kidding, his is pathetic.
Just in-case, I also bought it a natural black loop style tail. I still have the receipt and I have had my tail three years and I know it will last a long time