antique ball and chain shackles slavery black americana

up for sale is a vintage set of ball and chain and shackles. i was told by the auction that i got these at that they were used for transporting slaves off the ships. the ball is a 20 pound ball. enought to slow you from running i imagine but not too heavy that you cant be moved and brought off a boat. this is from missisippi. all forged chains ball and irons. questions please ask. very interesting item.