The semi-circular shackles are threaded on a bar secured by a T-shaped terminal at one end and a loop and twisted fastening on the other. These sort of U-shaped shackles were used to restrain captives while on board ship. They could be fitted over the ankles or wrists. Commonly, two individuals would be restrained together by one double shackle (the right ankle of one person would be shackled to the left ankle of another). The loops at each end slid onto a bolt of iron around a stock. An iron wedge was hammered into the stock to lock the shackles.

Enslaved people were only released for short periods of time, in order to eat or exercise on the deck of the ship.