Hard Nylon Clip snaps in track to hold the shutter panels open. The Base is 1 3/4" x 2" The circular track clip is 3/4" Diameter, made to fit a 1/2" Track. Sometimes its necessary to Trim these clips with a razor knife to fit properly fit the track type. For narrow tracks you may need to slice a toothpick size piece off each rounded clip so they close a bit more, to fit a 1/2" track. For tracks with no buildout you may need to slice the top flat part along the side. HV = Hi Velocity These Holdback clips fit a 1/2" bottom track snugly to hold accordion shutter panels open, and the curved top makes it easy to pull them out to close the shutter panels. Helps stop the accordion panels from Chattering in the wind. Some Accordion Shutter Panels have Locking Pins and holes in the track, to hold the panels open or closed,... you can use these Holdback Clips in place of those pins to make the accordion panels open wider to the frame, and Tighter to stop the Chatter in the wind.