This is a faceplate for the PT66ECI or PT66EI-24P prototyping board's ENC2015S-NZ enclosure when the SBC66EC or SBC66ECL board is plugged into it.
The faceplate is shaped to expose the SBC66's RJ45 Ethernet port, micro-USB port, status LED and power supply connector (with an SBC66ECL, this assumes you ordered it with the optional power supply connector). Markings provide details about the required power supply.
The left side of this faceplate is solid, so it only should be used if you have no iMOD modules plugged into your PT66 prototyping board. Faceplates with cutouts for various iMOD modules are planned but not yet available.