The specification discloses concrete forms each including a plurality of rectangular panels secured edgewise together by connectors. Each connector includes a pair of half sleeves secured in a pair of grooves in the edges of the panels, and a cupped head of a connector sleeve wedges the half sleeves...http://www.google.com.au/patents/US4211385?utm_source=gb-gplus-sharePatent US4211385 - Concrete form structure
