A corner piece for use in a spacer tube assembly includes a pair of arms each adapted to enter into and engage within an end portion of a respective spacer tube; hinge means defining a hinge axis and permitting said arms to be pivoted into a generally right angle relationship with each other; and friction means on each of said arms adapted to come into close contacting relation with each other as said arms are pivoted toward said right angle relationship to frictionally retain said arms in said generally right angle relationship.