This is an insert for the cup holder some Peterbilts have between the seats. I used measurements from a 2024 367 but I suspect most Peterbilt cup holders are the same size.

This allows you to put a 500ml/16.9oz water bottle or a 355ml/12oz pop can in the oversized cup holders without it falling out when you hit a bump.

Refer to the picture to see how the supports are placed. The larger ring is the top. I used superglue to attach everything.