a guide piece molded out of a rigid but slightly resilient material , such as plastic , having an elongated body with a u - shaped channel , used to hold an edge of a printed circuit card , extending the length of the guide piece to form an opening on each end . the guide piece has a plurality of raised tabs along the external surface of one leg of the channel and middle and end nubs on the external surface of the other leg of the channel . the raised tabs mate with fingers formed in a chassis , and the middle and end nubs mate with holes in the chassis . the combination of the raised tabs mating with fingers , and the middle and end nubs mating with the holes , secures the guide piece to the chassis , without requiring protrusions through the chassis .