Simple plastic coding keys are fitted into cavities in the back of handles on the plug-in board front panel and in the front of a range of guide rails installed in the subrack. Available in red or grey the keys are offset and if installed the same way on both the guide rail and the plug-in board, they will interfere, thus preventing insertion.
The IEC60297-3-103 compliant system can also be implemented for rear I/O transition boards. Although printed circuit boards of only 3U height are equipped with one handle at the bottom of the front panel, they can still employ 64 combinations of coding.
Compatible guide rails include red, yellow, grey and green for 160mm and 220mm plug-in boards, as well as the plastic front section for a 3-part guide, the aluminium centre section of which allows infinite PCB depth variation. They also include the rear transition 80mm guide rails and those designed for power supply usage in CompactPCI with a 1/2 HP offset.