I am going to buy a new knot for my Duke 2, but I don't know the knot size. I know that I can measure once I've removed the old knot, but I was hoping that someone with better tools than my plastic ruler had already done this. I've seen specifications that say it is 21/22 mm, but I'm not sure which number is the one that I should use in purchasing a new knot. Any help would be appreciated.