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.