Purchased from Interlocking puzzles 2002.
(13 ply Baltic Birch rings 7.2", Australian Jarrah rods 2.25", 18 pieces)
Four 6-piece burrs connected in one dimension by a pair of rings.
Requires multiple counter rotations of the rings to disassemble or
assemble. Interlocking Puzzles said:
"The eight radial pieces have slightly angled notches and can be sorted
into four right handed and four left handed pieces. The eight axial
pieces have normal notches. The four unique higher level burrs are
distinctly different. The lengths of the burr rods are greater than 6
units. If these were four stand alone burrs they would require five,
four, or three moves to get the first piece out. One of them would also
require three moves to get the second piece out. It is a fun challenge
to assemble each individual burr onto the rings and then remove it
before facing the larger challenge of the whole puzzle."
Solution sheets that came with the Berserk BurrCirc: