Really unique piece of mud from what I would suspect is Australia. Has Australia incuse embossed on the dome, and the rest of the embossing around the piece you can see in the collage. Looks to Fit on a standard CD 128 style metal pin. Nice light and medium brown color. Looks to have a crack in the insulator under the cap in the skirt WG, but nothing moves, is missing or is loose. Have no idea on the M number, but it sure is a neat looking bugger. $40 + shipping.