Fargo 84057 YMCKI ribbons are for either single or dual-sided printing. The YMC panels are used to print on the front of the card, while the black resin (K) panel and the inhibitor (I) panel can be used on either the front or back of the card. The I panel allows cards with surface foils (front of card), or signature panels (back of card) to be printed on by preventing the retransfer film from adhering to those areas. The main use of the I panel is when printing on cards that have a signature panel, since the film would make it difficult to write on.
The Fargo 84057 ribbon is for use with the HDP5000 series of card printers, and must be used in conjunction with HDP film for HDP5000 printers.