conceived to be place on a post , for instance that of a street - lamp , this support is constituted by two semi - clamps and , which include various radial flanges , those of one of the semi - clamps being equipped with toothed strips , and those of the other with grooves with a complementary tooth , in such a way that the clamp closes by mere pressure of one semi - clamp on the other with the interposition of the post . additionally , each semi - clamp includes a prismatic - rectangular housing , open at the top and sideways by means of an intermediate groove , where a prismatic - rectangular head is capable of being plugged , said prismatic - rectangular head finishing off each arm sustaining the advertising publicity poster , and being perfectly stabilized in the housing while the arm emerges outwards through the groove .