This is a Sensor Foot (Q) For Husqvarna Viking Group 7 Sewing Machines.
 
Husqvarna Viking Sensor Q Foot (413192045)The Sensor Q Foot is used for embroidery and free motion sewing, quilting and embroidery on especially thick or spongy fabrics. Put on the Sensor Q Foot for free-motion Quilting with puffy battings, free-motion and built-in embroidery on fabric with batting, thick terrycloth towels, and when there is a build up of embroidery thread or couched decorative threads.For best results it is recommended to use a single hole needle plate.Compatible machines:- (Group 7) Designer Diamond, Ruby, Topaz, Sapphire 960Q