These magnetic hold down brackets are used on sheer shades manufactured by Hunter Douglas and Levolor. They work with bottoms rails that are metal. 

Sold as a kit that contains two hold down brackets and two size #6 flathead Phillips mounting screws that are 3/4" long. 

Silver metal and clear plastic.

Hunter Douglas part # KIT9108.

To install these hold downs, follow these steps: 

Lower the shade, keeping the vanes closed.

Place the magnetic hold-down bracket onto the bottom rail just inside the end cap. Then, hold the bracket while opening and closing the shade (it may be necessary to have someone else assist you). Move the bracket up or down to the best position.

Mark the screw location with a pencil. The screw should be placed in the middle of the channel to allow for adjustment. 

Drill the screw holes using a 3/32" drill bit. Be sure to use drywall anchors (not included) if you're mounting into drywall. Attach the hold-down brackets to the mounting surface using the screws provided.

If necessary, adjust bracket height by loosening the screw and sliding the bracket up or down.