Apem standard membrane keypads apem ac3559 the apem 1 x 4 standard membrane keypad with insert pockets is a high quality matrix keypad with four pressure pads that have outlines and symbols printed on a flat flexible surface the clear windows have a silver perimeter embossing a silver unembossed border on a black background while two inserts with black graphics on a silver background are also supplied apem ac3559 standard membrane keypad 1x4 with insert pockets