An injection apparatus comprising at least one nozzle for injecting molten plastic into a molding cavity of a container, in particular of a test tube or a bottle preform; a molding cavity and a shutter for each nozzle; wherein the at least one nozzle comprises a component, the component comprising a first body in which a shutter can slide along an axis; wherein the first body defines an end portion of the nozzle and is provided with an opening from which the molten plastic can leave the nozzle, in particular to then enter the molding cavity; wherein the first body has a wall which extends about said axis; wherein said wall is provided with an inner surface having a first zone which is distal from the opening and is adapted to guide the sliding of the shutter along the axis, and a second zone which is proximal to the opening, which delimits a first stretch of a channel for the molten plastic and which delimits said opening; wherein said first body is provided with a plurality of through holes which cross said wall transversely to the axis, and which allow the molten plastic to pass through, in particular to enter, said first stretch of the channel; the component comprising a second body which delimits a second stretch of the channel which is distal from the opening; the first body being inserted in the second body so that the molten plastic can pass from the second stretch to the first stretch, passing through said through holes; wherein said first zone has a first diameter and said second zone has a second diameter which is greater than the first diameter, or wherein said first zone has a first diameter and said second zone has a second diameter which is greater than or equal to the first diameter, and the first body is made of a material having a lower thermal conductivity than the material with which the second body is made; wherein said second zone of the first body is proximal to the molding cavity and said first zone of the first body is distal from the molding cavity; wherein the shutter is adapted to pass from a closed position in which it prevents the molten plastic from passing through an opening of the molding cavity, to an open position, and vice versa; the injection apparatus being configured so that the shutter is guided by the first zone of the first body both when passing from the closed position to the open position and when passing from the open position to the closed position; wherein in the closed position the end portion of shutter, which comprises the tip of shutter, obstructs the opening; wherein in the open position, the end portion of the shutter is surrounded by the first zone, leaving the outlet section of the through holes at least partially free for the molten plastic to pass from the second stretch to the first stretch. wherein the at least one nozzle comprises a component, the component comprising a first body in which a shutter can slide along an axis; wherein the first body defines an end portion of the nozzle and is provided with an opening from which the molten plastic can leave the nozzle, in particular to then enter the molding cavity; wherein the first body has a wall which extends about said axis; wherein said wall is provided with an inner surface having a first zone which is distal from the opening and is adapted to guide the sliding of the shutter along the axis, and a second zone which is proximal to the opening, which delimits a first stretch of a channel for the molten plastic and which delimits said opening; wherein said first body is provided with a plurality of through holes which cross said wall transversely to the axis, and which allow the molten plastic to pass through, in particular to enter, said first stretch of the channel; the component comprising a second body which delimits a second stretch of the channel which is distal from the opening; the first body being inserted in the second body so that the molten plastic can pass from the second stretch to the first stretch, passing through said through holes; wherein said first zone has a first diameter and said second zone has a second diameter which is greater than the first diameter, or wherein said first zone has a first diameter and said second zone has a second diameter which is greater than or equal to the first diameter, and the first body is made of a material having a lower thermal conductivity than the material with which the second body is made; wherein said second zone of the first body is proximal to the molding cavity and said first zone of the first body is distal from the molding cavity; wherein the shutter is adapted to pass from a closed position in which it prevents the molten plastic from passing through an opening of the molding cavity, to an open position, and vice versa; the injection apparatus being configured so that the shutter is guided by the first zone of the first body both when passing from the closed position to the open position and when passing from the open position to the closed position; wherein in the closed position the end portion of shutter, which comprises the tip of shutter, obstructs the opening; wherein in the open position, the end portion of the shutter is surrounded by the first zone, leaving the outlet section of the through holes at least partially free for the molten plastic to pass from the second stretch to the first stretch.