2" dia. brass frame has large aluminum knob at center and pair of small cut-outs through which either a number or letter shows. This is the scarcest of the decoders as the reverse is a dark red plastic cover held by means of two small internal tabs so frequently the decoder back was lost. Center of the back includes a glossy silver luster rectangle of metal to be used for signaling purposes. Very tiny warp on the plastic back but holds firmly into position as it should. Front of the piece has gorgeous N. Mint brass luster. N. Mint and about as nice as they come.