Abstract: Hollow plastic posts and rails interlock to form fences. The posts are hollow cylindrical pipes having two axially spaced elongated ovalur slots through the shell thereof for receiving the rails. The rails are hollow plastic members having ovalur ends for mating into the slots on the post. The members are interlocked by forming flexible deformable rail ends with a width slightly greater than the length of the receptacle slots and notching the rail ends to register in place engaging the shell casing of the posts at the ends of the slots.