I am trying to create a ring for 3D printing. Part of the requirements for 3D printing is to not have any non-manifold geometry in your model. When checking whether I met this requirement, I found that my model contains two edge loops consisting of "Boundaries" non-manifold geometry.
Highlighted in orange are the non-manifold edges of type "boundaries" (Highlighted using Ctrl + Alt + Shift + M, only Boundaries is toggled so that I could narrow down what type of non-manifold this is):
I undo that translation, reselect the non-manifold edge loops through Ctrl + Alt + Shift + M, and I "Remove Doubles". Here, I find that the hidden duplicate loop no longer exists, but now my non-manifold edges are of type "Non Contiguous":
Honestly, I am new to 3D Modelling and Blender, and am not sure how to correct my issue from here. Do you guys have any advice?