The gap is lengthwise, as seen below. The kit has parts to wrap the dowel in, but if you use the size of dowel I did, you have a gap. An unfortunate bit of ugliness, but easy enough to cover up to make it unnoticeable.
The diameter of the rod is unavoidable for me -- it's the only one that wouldn't be too small, which would be completely unworkable. Better too large than too small.