Abstract: A knockdown spacer for bookshelves and the like which is made from a single elongated rectangular blank of sheet material, creased at spaced intervals to fold into an open ended box-like block with internal diagonal bracing walls. The outer walls of the box structure wrap around the diagonal braces and one end of the blank has a retaining flap which overlaps one of the walls and is secured by releasable fasteners. The blank can be made at minimum cost from corrugated cardboard, or the like, which can support heavy loads when formed and braced in the manner described.