Update - added the STL files.

UPDATE : uploaded new and improved versions that include all connector types and work together. I was tired of the misalignment between the carton pieces and the new printed ones, so decided to print all the borders.

Bought the basic Catan set in the US, then bought the Seafarers' extension in Israel. Found out the border pieces in both sets are incompatible with each other, as they have different connectors. I looked for existing pieces in Thingiverse to match either sets, but could not find good ones, so I decided to create them The pieces here are the pieces that match the Seafarers' extension but match the original Catan set. To save on material, I printed it at 2mm thick, but sometimes increasing to 3mm will provide more stable results.

Enjoy.