Abstract: A sector plate for a regenerative air preheater has an outer support ring centered on an axis and normally of cylindrical shape, an inner support ring centered on the axis, and a plurality of radially extending walls lying generally in axial planes and having outer ends fixed to the outer ring and inner ends and guided on the inner ring. A plurality of angularly extending and radially spaced annular walls extend between the radial walls and form therewith axially throughgoing passages. Thus when hot gases flow in one axial direction through the passages they thermally deform the radial walls so that their ends move into a position at an angle to each other. The ring is thermally deformed to a taper equal to twice the angle for holding the inner ends of the radial walls and the inner ring in the axially level with the outer ring when hot gases flow through the passages.