Lower cover

Abstract

The lower cover, containing through holes, is characterized by 12 pairs of through holes (1), arranged symmetrically along the longer edges of the upper surface. The upper surface is an elongated rectangle with a notch on the first, shorter side and extensions arranged symmetrically along the long sides, resembling butterfly wings, in the central part of the upper surface. Beneath the upper surface, a short distance away, is the lower surface, permanently connected to it and located parallel to it. Alternately, thresholds are arranged on its upper side. Their arrangement is transverse to the length of the lower surface and along its entire length. Furthermore, the upper surface has three sections of holes and an additional hole (8) on its second shorter side.