A stone-paved path leads to Morezmore Studio.
Inside you find:
Humanly Posable Armature (HPA) Parts
4-Hole Threaded Connectors
for Chest and Hip connection
Pack of 4
Thread: M2 (on both ends)
Drilled Center Hole Diameter - 2 mm
Humanly Posable Armature General Info and Instructions
The listing offers what you see on the first photo (4 connectors). Other parts on the second photo are shown for illustration purposes and are available for purchase in other listings.