Abh mod/Structure Segment 25-2-1Cc
The Structure Segment 25-2-1Cc was introduced in 0.3.9. It is the concave version of the Structure Segment 25-2-1.
The original idea and suggestion was turned down the previous year. As a result it was decided to add such aesthetic parts via a mod. The delay is due to the sheer number of parts and sprites required for the whole set.
Just place it like any other part.