Speed fastener captive nuts. Captive Nuts clip onto the edge of sheet metal. They are shaped like the letter U and are used in panel assembly. Standard Captive nuts are inserted into punched or drilled holes in sheet metal and other thin, soft materials. They act as both lock washer and nut, which eliminates the need for lock washers. Also called speed clips, spire clips, chimney nuts, U nuts, and captive nuts. Carclips has a large range of Speed clips to suit most automotive applications