How to close an open extrusion

I’m having difficultly figuring out a way to close an open extrusion. Any help much appreciated. Picture below

Well, your image is not very illustrative, but if I take it that the “open extrusion” is the little “U” shaped thingy…

In order to close that object, you need at least 3 surfaces, one each for the vertical sides and one for the “top”. As the original generator curve appears to be planar, you could simply create a planar surface between the two top ends of the “U” surface - using Loft between the edges or maybe just a rectangular plane - join the top surface to the “U”, then use Cap planar holes from the solid menu.

Or, even simpler, with your original profile curve - if you still have it - draw a line between the top ends and join to create a closed figure, then Extrude planar curve from the solid menu to create a closed object.

In general here is is best to post a Rhino file and not just an image, you will usually get better and more accurate help.



Appreciate your response. This answers the questions I had and will post file next time. Thanks again.