(Note: Measurements are outside max. dimensions unless stated otherwise).20th Century : Raised hollow square platform backplate with 'pastry cut' scalloped edge.FLANGE:29mm. x 29mm. (1 1/8" x 1 1/8")RAISED PLATFORM20mm x 20mm. (3/4" x 3/4")Diam. hole 7mm. (1/4")Total height 7mm. (1/4")Possibly originated from base to a lamp column.