An injection molding device for injection molding a flexible sleeve body for a squeezable tube, comprises a male mold part and a female mold part, which in combination with the male mold part forms a sleeve body cavity for forming the flexible sleeve body between them. The sleeve body cavity extends from a top end to an opposite bottom end in a longitudinal direction. The molding device further comprises a runner end part, which in combination with the female mold part and the male mold part forms a runner cavity at the top end of the sleeve body cavity. The runner cavity comprises a passage constituted by one or more openings connecting the annular shaped distribution channel with the sleeve body cavity for guiding the molten plastics material from a runner distribution channel into the sleeve body cavity. The one or more openings is/are evenly distributed along the perimeter of the sleeve body cavity and is/are narrow compared to the distribution channel upstream of the passage, such that the passage initially prevents the flow of molten plastics material from entering the sleeve body cavity, which results in a pressure build up in the runner cavity which eventually results in a pressure high enough to force the flow of molten plastics material through the passage into the sleeve body cavity.