12 1/2" ruler

[Hulamoon]

A square ruler will always be a square so it won't matter what one you use. Where it matters is how wide your fabric is so the size you have reaches the the other side of the tube. If you have a four strip tube use a bigger ruler , a smaller strip use a smaller ruler. It's just for convience.

Here is another tut on the same thing
http://www.youtube.com/watch?v=kVd9CfUK5gU

[WendyI]

Perfect! I figured out to put the diagonal on the seam line!

[judylg]

I have the 12 1/2 ruler. I use it more than any other I have. I recommend it!

I agree, the 12 1/2 ruler is one I use all of the time. If something happened to it, would replace with another I like it that much.