Two chests linked together, they have the storage capacity of a single chest but anything you add/remove from one chest appears in the other. You can only link a chest to one other chest and they can only be created in pairs. Reduced storage capacity as you can only have a small (single) chest.
Formula:
R - redstone
G - glowstone
C - chest
A - advanced circuit (we don't use them enough!)
RGR
CAC
RGR
