A teatcup liner comprising an upper mouthpiece, an intermediate barrel and alowerconnecting tube, wherein: the upper mouthpiece further comprises a mouthpiecetransition, amouthpiece lip, and a groove formed in an outer surface of the uppermouthpiece, saidintermediate barrel extending along an axial direction for receiving a teatinserted axiallythereinto through said mouthpiece； and an inner dimension of the uppermouthpiece definesa cavity bore and the groove is located substantially in line with the largestdiameter of thecavity bore.
