Hi telnoi - just one other note - if you use Edit/Join to join those surfaces to have a shared edge those small visual gaps between the surfaces should go away because they will then get a display mesh that has the same vertex structure along those edges.

When surfaces are separate individual objects, they get meshed individually and that can generate different numbers of polygon vertices along those edges (there are polygons created for the shaded display of the surfaces), that can make that kind of an appearance.

But that is just a display artifact and does not mean that your actual NURBS surfaces have cracks between them. For more accuracy it is better to go by what the edge looks like, and it looks like the edges between those surfaces you show are well aligned and overlapping.

- Michael