A common problem assembling the Hero Me gen 5 fan duct suite is the large number of captive nuts that just fall out while you are trying to assemble it.
These 2 tiny pieces (mirror images of each other) greatly reduce the problem.
Prior to use prepare the 2 pieces by running a M3 tap (or M3 screw if you don't have a tap) through the 5 deliberately undersized holes in each piece to cut a crude thread.
Where the Hero Me Base attaches to the gantry adaptor each side of the base has 2 captive nuts and 3 captive nuts for the duct attachment. Insert these 5 nuts, securing each temporarily with a screw but don't allow the screw end to protrude from the nut. Insert the appropriate Nut Keeper to cover the nuts, thin 3 holed section over the fan nuts, 2 holed thick section over the gantry nuts.
Screw in the duct screws all the way through the nut keeper, do the same for the gantry screws. Repeat for the other side.
The nuts are now captive and won't fall out (unless you remove all 5 screws).
Assemble the Hero Me leaving the NutKeepers in place just make sure that each side has either gantry screws or duct screws depending on which stage of assembly you are at