When the width of your open mouth isn't enough, the Fetish Fantasy Extreme Spider Gag will do the job.
This extreme level gag consists of a metal ring with curved metal legs attached to the ring.
The ring and legs prevent the mouth from closing, leaving your mouth wide open to fit anything you want. The ring's diameter is 1.5 inches, and the gag is attached to a leather strap that fastens at the back and holds the gag firmly in place.