Although once produced in a wide range of sizes (from less than to more than in diameter) and sometimes with glass core discs, the examples most commonly encountered today are in diameter and consist of an aluminium core disc coated with black nitrocellulose lacquer, commonly but incorrectly called "acetate". Instantaneous disc history authority Michael Biel attributes the longstanding "acetate" misnomer to some early lacquer disc labels that carried the warning, "Use only acetate needles", meaning the same high grade of individually inspected steel needles required to safely play the easily needle-damaged "pressed" flexible acetate transcription discs that were sometimes used in US broadcasting in the 1930s.