Blow molding of plastics to form hollow shapes such as bottles, containers and the like is well known to those having ordinary skill in the art.  Some shapes, however, are difficult to mold into a hollow container with a blow molding process.  An example of a shape that is difficult to mold is an indented female connector having a set of internal ribs for engaging with a male connector.  Accordingly, there is a need for an improved device for molding an indented female connector as part of a hollow object. 
Additionally, there is a need for hollow molded objects that can be assembled into sturdy durable structures, such as chairs, tables, stools, walls, and the like, without the need for extra components.  There is a need for these structures to be sturdy, so that they can withstand loads imposed on them without breaking or collapsing.  There is also a need for the hollow molded objects to be formed such that they can be repeatedly manually joined and released from one another without the use of tools, wrenches, additional components, hammers, screw drivers, and/or power equipment.