radially disposed grooves on the panel and three oppositely disposed grooves on the frame that supports the tensed mask three spherical balls serve to align the panel and the frame in a precise relationship the balls are permitted to roll in the grooves and one of the grooves in each pair is shorter than the other to restrict the range of positions of the ball in the other groove of each pair when the panel and frame are in the precise relationship application_number US 69307885 A description referring to fig1 a flat glass panel 10 of a crt includes on the inner surface thereof a target 24 conventionally consisting of a regular pattern of elemental colored light emitting phosphors arranged in clusters or triads each comprising a red blue and green phosphor element positioned adjacent to target 24 is a flat shadow mask 22 which as is well known in the art includes a plurality of apertures for masking or shadowing different ones of the elemental color phosphors in target 24 from all but its assigned one of a plurality of electron beams emitted from a gun structure 18 located in an elongated neck 16 of the crt mask 22 is maintained in position adjacent target 24 on the inner surface of panel 10 by a frame 12 the forwardly directed surface of which is sealed to panel 10 by glass 34 frit 34 26 a generally bell shaped funnel 14.