A cartridge (1 ) and a teatcup to be attached to the teat of an animal to be milked are disclosed. The cartridge comprises an elongated sleeve (20), having an upper end section (20a) and a lower end section (20b), and a teatcup liner pre-mounted in the elongated sleeve. The teatcup liner comprises an upper end portion located at the upper end section, a lower end portion located at the lower end section, and a barrel portion extending between the upper and lower end portions. The barrel portion has a polygonal cross-sectional shape defining a plurality of corner portions and a plurality of side portions. The elongated sleeve comprises a primary locking member (28). The teatcup liner comprises a primary complementary locking member (29). The two locking members engage each other to prevent rotation of the teatcup liner in relation to the elongated sleeve.
