A tube fitting for a large diameter tube comprises a coupling body having a bore, a counterbore adapted to receive such tube, and a rearwardly opening generally frusto-conical camming mouth adapted to surround the tube when inserted in the coupling body. A front and back ferrule are provided which are adapted to be snugly received upon the tube. The front ferrule is defined by a nose portion adapted to engage the camming mouth. The rearward end of the front ferrule is provided with a camming mouth adapted to be engaged by a nose portion of the back ferrule. The rearward end of the back ferrule is provided with a back face adapted to be engaged by a complementary surface of a coupling nut which is threadedly engaged with the coupling body. The relationship of the parts is such that the axial length of the front ferrule has a minimum value which is a function of the tube outside diameter so that the wave induced in the tube by the front ferrule on make-up of the fitting is not encountered by the nose portion of the back ferrule.
