The invention relates to a stretch rod used for forming a preform into a hollow body having in its surface a plurality of raised portions and/or recesses relative to the circular cylinder shape, whereby the stretch rod tip can come into contact with the concave, rotationally symmetric inner surface of the preform at a plurality of locations which are separate from one another. Also, the invention relates to a method and an apparatus for forming a preform into a hollow body, which uses such a stretch rod.