MeshToNURB is usually not useful to convert mesh objects to NURBS objects. MeshToNURB creates a separate NURBS surface from each mesh face.
The object in your file has simple geometry so in a few minutes I recreated the geometry as a NURBS objects.
I drew curves on the edges of one face.
Vertex OSnap On.
Drew the circles using Circle with the 3 point option snapping to vertices.
Drew the straight edges with Line snapping to the veritices.
Split the circles on the out edges using the lines, Discarded the un-needed parts.
Joined the remaining arcs and straight lines into a polycurve around the outside edge.
PlanarSrf using the edge curves to create one surface.
Measured the thickness.
ExtrudeSrf to create the solid.
mesh_to_nurb_DC1.3dm (12.9 MB)