The Panel Joint consists of locking pin and locking arm on opposite edges. It is all plastic or steel and has great strength and no complicated ribs are needed. The panel joint is inlaid into panels during foaming. The panels can be connected closely when you turn clock-wise the panel locks by special tool which is provided with the cold storage. To expand the cold-storage volume, you can simply remove the panel where size increasing is desired turning the panel lock back from our works. It is easy to enlarge prefab cold-storages quickly.