This air assist fan replaces the small fan at the back of the carriage plate on the Glowforge. This is the 40mm x 40mm fan that sits behind the laser head and prevents flames when cutting and engraving. If it's extremely dirty or the blades get damaged it will often cause large flames and issues cutting. If there is a short in the circuit or one of the wires are damaged it will often cause an error that will prevent projects from loading. If you were to stock any part for a rainy day for your Glowforge this should be the part. Fan only.