An injection moulding machine comprising - a frame; - an injection unit attached to the frame; - a clamping unit being attached to the frame; and - a linear drive mechanism for moving a second mould plate of a mould box of the clamping unit, wherein the clamping unit comprises - a clamping unit frame; - a base plate fixedly arranged at a first end of the clamping unit frame; - a second end structure fixedly arranged at a second end of the clamping unit frame; and - a mould box, wherein the mould box comprises - a first mould plate; - said second mould plate movably arranged relative to the first mould plate along a longitudinal axis; and - a main guide rail system configured for guiding the second mould plate linearly away from and towards the first mould plate when moved by the linear drive mechanism of the clamping unit, wherein the main guide rail system comprises only one main guide rail pillar, wherein the main guide rail pillar comprises a first end and a second end, the first end of the main guide rail pillar being fixedly connected to the base plate of the clamping unit, and the second end of the main guide rail pillar, being fixedly connected to the second end structure of the clamping unit, and wherein the main guide rail pillar has a cross section perpendicular to the longitudinal axis, and wherein the cross-section forms a polygon. - a frame; - an injection unit attached to the frame; - a clamping unit being attached to the frame; and - a linear drive mechanism for moving a second mould plate of a mould box of the clamping unit, wherein the clamping unit comprises - a clamping unit frame; - a base plate fixedly arranged at a first end of the clamping unit frame; - a second end structure fixedly arranged at a second end of the clamping unit frame; and - a mould box, - a clamping unit frame; - a base plate fixedly arranged at a first end of the clamping unit frame; - a second end structure fixedly arranged at a second end of the clamping unit frame; and - a mould box, wherein the mould box comprises - a first mould plate; - said second mould plate movably arranged relative to the first mould plate along a longitudinal axis; and - a main guide rail system configured for guiding the second mould plate linearly away from and towards the first mould plate when moved by the linear drive mechanism of the clamping unit, - a first mould plate; - said second mould plate movably arranged relative to the first mould plate along a longitudinal axis; and - a main guide rail system configured for guiding the second mould plate linearly away from and towards the first mould plate when moved by the linear drive mechanism of the clamping unit, wherein the main guide rail system comprises only one main guide rail pillar, wherein the main guide rail pillar comprises a first end and a second end, the first end of the main guide rail pillar being fixedly connected to the base plate of the clamping unit, and the second end of the main guide rail pillar, being fixedly connected to the second end structure of the clamping unit, and wherein the main guide rail pillar has a cross section perpendicular to the longitudinal axis, and wherein the cross-section forms a polygon.