Klaws,They are cloth( such as duck cloth) that is used to pin the backing, batting and top to in a quilt frame.These cloths remain on the frame in different lenghts on the different poles.The backing is the first to be pulled up ,to the top take up pole and these leaders are what the backing is pinned to,and ect.The" marked"leaders have lines in inch or so intervals.Use to help square quilts with and keep them running straight while you quilt them.If my answer has completely messed you up you can google how to load a quilt in a frame,and you will see and understand better. Sometimes when I load a quilt in the frame to quilt, I find my backing; even when I use straight edge, my backing on one side wants to be a tad bit floppy like it is not squared up I am worried this will make my quilts look warpped.So that is why I ask if marked leaders are helpful and worth the extra money.Hope this helped.