Felen only standardized texts (as required by magic), but did not standardize the rails for the carts, not to mention standardized parts. It's not just that different countries and different workshops produce different products, even carts produced by the same craftsman might differ significantly in size.
Thus, a multitude of different types of carts travel on Felen Trade Routes, and from time to time, you'd see graveyards of carts beside the routes, with relatively new carts discarded inside, all for the want of a unique-sized wheel that had broken beyond repair. Unable to find a replacement on short notice, and not worth the time to have one custom made, the carts are abandoned with a heavy heart.
