Inside the slipcase - Variant C.

This construction method was used for the sixth state of the slipcase.

In use 1961 to 1964.

The slipcase is made from two partial slipcases.  Each piece has the top, rear and base panels and one side panel.  They are overlapped and stapled at each corner of the top and base panels.  The overlapping rear panels are held together by the paper covering material.

This type of construction should (in theory) be stronger than the earlier one and three piece designs, but many of the boxes were made were too large, meaning that the books could move around inside.  This allows the slipcase to twist, making it susceptible to splitting.