Edison Diamond Disc

Diamond discs were a type of gramophone record marketed by by Thomas A. Edison, Inc. on their Edison Record label from 1912 to 1929. They were named 'Diamond Discs' because the matching Edison Diamond Disc player was fitted with a permanent conical diamond stylus for playing them. Diamond Discs were incompatible with lateral-groove disc record players, e.g. the Victor Victrola, the disposable steel needles of which would damage them while extracting hardly any sound. Uniquely, they are just under ​1⁄4 in (6.0 mm; 0.235 in) thick.