Charles Ellicott Commentary Exodus 26:4

"And thou shalt make loops of blue upon the edge of the one curtain from the selvedge in the coupling; and likewise shalt thou make in the edge of the curtain that is outmost in the second coupling." — Exodus 26:4 (ASV)

From the selvedge in the coupling. —Rather, at the coupling. The selvedge, i.e., nearest to the place where the two curtains were to be coupled together.