When coins are being struck, the lower die (reverse die) is surrounded by a collar. This collar floats on springs, which prevents damage to the coinage press, if there is a malfunction. When a planchet is fed into the coinage press, it should rest inside the collar on the reverse die (lower die). If the planchet does not rest completely inside the collar, you will have an Off Center struck coin. Only part of the coin will show the design. Since the collar floats beside the die, it is pushed down if the planchet is resting on the collar during the striking process