This limit stop is for Hunter Douglas Silhouette shades. It prevents the shade from over-rolling when it is rolled up.
This part has been used since May 2008 for 2″ Silhouette and all 3″ Nantucket fabrics.
It works on shades with a tube that looks like this:
White plastic.
Sold individually.
Levolor Sheer Shadings also use this piece for their cord loop, retractable cord, cordless, and motorized shades.
Hunter Douglas part # 4150057885.