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STEP 5 - FIX THE CENTRAL JOINT
A central joint would come into being after you finish Step 4. Put a
part #E, a part #H, and a
part #K into the central point
, tighten them with the tools (parts I and J).
IMPORTANT:
if you feel it is a bit difficult to finish assembling the last joint of each layer,
slightly loosen the bolts of two adjacent joints.