This is an interface for adding a USB hub with built-in SD and micro-SD card reader, and audio cable ports in two different sizes, to the right end of the keytar case. The part that holds the audio cables also covers where all the cables pass through the hole in the end of the case (where the cable for the original keytar originally came out). The 3 smaller holes that are already in the case are used for anchoring the hub to the case, and a couple more holes will need to be drilled in for the cable cover. The U piece is to help secure the regular audio cable in place, with a bit of glue after painting and install. There are a couple points where I'm not entirely happy with the fit, but it's close enough, and they are small enough issues that when I paint it might fill them in. If you like my designs and makes, please visit my blog at https://technomancers-sanctum.blog/