An apparatus for supporting a preform is provided. The apparatus comprises a shaft defining a groove. A deformable element is arranged in the groove. A split ring having at least two pieces is provided. Each of the pieces has an inner surface facing the deformable member and an outer surface. At least one of the pieces has a protrusion extending from its inner surface. The protrusion is arranged adjacent to the deformable element and the split ring being moveable in a radial direction whereby the protrusion causes the deformable element to be compressed in the groove.