Basically it covers modifiers for standard 87/88, 101/102, 104/105 like G80-1000/3000, Filco, Leopold, Ducky, etc., 101/102 and 104/105 G80-1800, Choc Mini, Poker, Pure, and so on. So essentially the majority of MX keyboards that follow ANSI, ISO and JIS except for the backspace.