"The border of the 4th edition Settlers of Catan is too small for the board hexes. To be exact, each hexagonal tile is about 79 mm wide. Five of them, end to end, form the longest stretch of land requiring 395 mm of width within the shore tiles. And now, the distance between the shore tiles? About 393 mm. Yup, 2 mm short." http://www.tinysci.com/2010/07/04/the-settlers-of-catan-something-completely-different/
Lots of custom boards out there because of this problem.
Is there an inexpensive commercially-available border that actually fits?