Method of producing hollow profiled preforms for passages in building walls

摘要

One of the outer recesses on the inside of the preform (21) forming a support (213) leads into one of the end sides (211) of the preform. The recess formed on the periphery of the preform and adjoining the end side (214') facing the end side of the preform with a support leads into the adjacent end side when the dimensions agree with the recess forming the support. The preform has a peripheral shoulder (216) protruding into the preform, on the end side facing the end side with the support.