This is a set of two Sashers - one is 1-1/4in and the other is 1-1/8in - depending on the cut size of your fabric. You are right - 2-1/2in strip of fabric needs a 1-1/4in sasher to feed through to a finished size of 1-1/4in. The 1-1/8in sasher is for a 2-1/4in fabric strip (some like the slightly smaller binding.)
- The fabric size is ALWAYS double the Sasher size.
- The Sasher size is ALWAYS the finished size of the pressed fabric strips.