This is a reproduction Hamburg 8 handcuff. They come with a single key. These are made of nickel plated brass. High quality construction and finish made in Pakistan by KUB Industries. When folded (only in one direction) the cuff mechanism allows the cuffs to be opened. When fully extended, the bows, when pressed down, will lock. To unlock the cuff a key needs to be inserted into the lock case. The key pushes the bolt out of the way and allows the cuffs to open.