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

In use in 1961 only.

The slipcase is made from a single piece of board.  This is folded to form the slipcase and then stapled at each corner of the top and base panels.  Finally it is covered with the paper covering material.  The orientation and exact positioning of the staples varies.

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