Gussets are the most common connector here at Framing Tech.  They allow the fastening of two pieces of extrusion at a 90° angle without the need for machining.  One of their features is an alignment tab that helps hold the position in the T-slot, and also prevents the gusset from rotating.  The mounting holes for most of our gussets is slotted, which allows for some "wiggle-room" when adjusting your positioning.  Common uses for gussets are for mounting table tops from underneath, fastening a machine frame to its base, installing a divider wall, as lift points for counterbalance systems and much more!