Make Solid? Lines to round object?

[Tobbeswim]

Hi,

I am brand new to SketchUp. The program looks fantastic but I have some issues with my drawing. I am going to 3D print speaker-grills that I will attach speaker cloth too. My problem: I can not make the frame solid and I can not make the cross-netting lines thick solid. The lines that is right now just lines should be 2mm x 2mm round (or square, does not matter) solid objects that holds the top frame (also need to be solid) in place.

How do I do this? Do I need to do it from scratch with some different setting or could I fix it on this drawing?

Please help!!

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Speaker grill