2.25" tall brass case which was made with no pin for wearing. Bottom edge has red notched plastic wheel which turns to show letter and numeral combinations in a pair of small cut-out center windows. Above the window is a slot for a tiny brass key which was used to set various combinations. The keys are much scarcer than the decoders as most kids quickly lost them. Both the decoder and key have brilliant luster Mint as made. A superb example, best we've seen in five decades.