The figure below shows the principle correlation between the wall thickness and the shrinkage Due to the lower wall thickness, ejection grooves may appear in the lower periphery at identical drafts. In the case of insufficient mould stiffness or excessive mould deformations due to excessive cavity pressures(possibly pressure peaks), ejector grooves may also appear on the lateral surfaces. The reason is the weak dimensioning of the injection mould transverse to the direction of closing. This is then known as an inadvertently large lateral mould cavity expansion. Predestined for this are