Hello adldesigner ! Thank you again for your wonderful support - that´s really fine, and also thanks to all other user in this forum for helping me, like mike. :banana: Now I understand why it´s important to have the same spans from opossing curves, and how I can get it. And I also know how I can get the same direction. I fulfilled your very important two lections in my example. But now I was very surprised - why ? 1. I´ve created the first surface with birail 2. Very well, all okay. I´ve got the follwing UV SPANS 1/4 2. After that, I created the 2nd surface with birail 2. And here I´ve got a surface with the follwoing UV SPANS 5/4. Is that okay ? thx for helping me and best wishes, Bernhard