US Patent 10520118 Tube fitting assembly

A fitting assembly having a longitudinal axis including a fitting body having a seat, a threaded drive nut, a tube, a first (rear) ferrule and a second (front) ferrule receivable over the tube, the first (rear) ferrule having a first driven end and a first driving end and defining a first (rear) ferrule length (FFL) therebetween, the second (front) ferrule having a second driven end and a second driving end and defining a second (front) ferrule length (SFL) therebetween, and a seal depth (SD) of the tube defined by a distance between the seat of the fitting body and the second driving end. A surface of the second driven end of the second (front) ferrule is a diametrical surface having a diameter (DSF). At least one of the following apply:SFL/SD≥0.9;2.7≥SFL/DSF≥2.2; andSFL/FFL≥4.0.