A frame corner member includes an elongated hollow extrusion having a central corner portion and two leg portions extending from the central portion. Each leg portion includes an inner side wall spaced from and parallel to an outer side wall, and merging with the central portion. An outer end wall joins the inner and outer side walls, which each include an inner surface facing the inner surface of the other side wall. An opening through the outer end wall defines a space between the inner and outer side walls adjacent one end of the extrusion for receiving one end of one of frame side members and end members. At least one of the inner surfaces in the space has discrete surface features adapted to grip and retain the one end of one of the side members and end members in the space when received through the opening.