ND120 absorptive neutral density filters have an optical density of 1.2, averaging 6.25% transmission over the visible spectrum. These filters include identical male and female threads on either end so that they can be stacked with other ND filters to achieve various optical densities. For example, the result from stacking two ND120 filters together would be very similar to utilizing one (ND240) filter. Visible transmission would approximately equal 0.4% of visible light.