This is an Arri Full Double Scrim that fits the 150W Fresnel or any fixture that accepts a 3" accessory. Scrims are metal screen mounted in a metal frame. They are placed in front of a light to reduce light intensity. Arri makes four different types of scrims. Full single- this scrim covers the entire lightface and reduces the intensity of the entire light beam. Full double- again this scrim covers the whole face of the light. It has two metal screens in it, reducing light intensity by two times the amount of the full single. Half single- this scrim only covers half of the lightface reducing half of the light beams intensity. Half double- same as the half single but reduces light intensity twice as much as the half single.
Half scrims may be rotated in position, for more precise control.