This burner is specifically made for the small flue models. Typically 1/2" to 9/16" ID flues. These are drilled with an additional pair of air holes to aid in proper combustion with the confined flue.
Thse have a small flange and no extra cutouts. The Ruby based models along with many other models use this size flange.
All burners include a jet holder with a M5 threaded nipple for direction connection to the stock gas fittings along with a new premium no5 jet.