While Rosco acquired GAM in 2013, the GAM legacy lives on in their popular range of gobos.
 

Gobos are like stencils for profile (ERS-style) lighting fixtures, allowing light to shine through certain areas and project a pattern. The color of the projected image can be changed by adding a sheet of lighting gel, or by changing colors on most LED fixtures. By adding a donut (color frame with smaller hole) you can increase the contrast and clarity of the projected image. Full-size Source Four fixtures also offer EDLT and XDLT lens tube options designed for the highest quality gobo projection.

The size of a projected gobo image depends on the beam angle of your fixture, a larger beam angle will increase the gobo size diameter, however the resulting image will appear dimmer (with same fixture, since the light is spread over a larger area). Gobos come in many different sizes for a range of fixtures, the table below gives a summary of the most common sizes that we list online.  

GAM Gobos - Datasheet  |  GAM Gobos - Instructions