The Small Iris card is the size of a standard business card 3.5" x 2". It functions as a mechanical iris similar to those used in photography aperture mechanisms. A tab on the card can be manually rotated to progressively open the hole in the center of the card up to a maximum size of one inch. The card varies in thickness, but is approximately .09" thick at its thickest point. See the video below for a demonstration of the card. This listing is for the fully assembled card; the kit version that need assembly can be found here.