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 all 3" Silhouette fabrics, Quartette 4" fabrics, Chateau fabric, and Grandiose shadings. 

It works on shades with a tube that looks like this: 

White plastic.

Sold individually.

Hunter Douglas part # 4140126000.