Why are my edges naked?

basic2.3dm (1.5 MB)
I can’t see why these naked edges exist.

I have removed all the loops, aligned the edges up nicely, but still get “Unable to find overlapping intervals.” when I try and join the naked edges

I’ve tried trimming behind the naked edges, only to produce more.

I am stumped, any help appreciated, cheers

Hello - ‘naked’ edges are any surface edges that are not joined up to some other surface edge - your file has just a single surface - zero thickness - that has two long nakeds and two ‘singular’ ones at the points - this is expected and normal until you get another surface in there to join up to and close off a volume.