Abstract: A corner piece for connecting the ends of two adjacent spacers in a double glazed window unit, each spacer being formed from a metal strip bent into a hollow elongated form and having the edges forming an internal joint, the joint including one edge portion of the strip bent to form an outwardly facing groove and another edge portion of the strip bent to form an inwardly extending lip which is of lesser depth than the groove. The corner piece has two arms extending at 90.degree. to each other, each arm having a base and two side flanges and being suitable for fitting in the end of an adjacent spacer. Said base of each arm has an inwardly angled extension having a recess at its outer end capable of receiving the edge portion of the strip which forms the groove to prevent spreading of the groove when the corner piece is inserted into a spacer.