Research calls this a rattle Shackle. When you shake it rattles rattle. Notice on the Shackle it has Mark's on it which I don't know the meaning of. Also you can see the metal rattle. The item "Mid 18th century Slavery Crab Rattle Shackle Authentic original pre civil war" is in sale since Tuesday, July 16, 2019.
This item is in the category "Collectibles\Historical Memorabilia\Other Historical Memorabilia". The seller is "jcm2223james" and is located in Shelbyville, Indiana. This item can be shipped to United States, Canada, United Kingdom, Denmark, Romania, Slovakia, Bulgaria, Czech republic, Finland, Hungary, Latvia, Lithuania, Malta, Estonia, Australia, Greece, Portugal, Cyprus, Slovenia, Japan, Sweden, South Korea, Indonesia, South africa, Belgium, France, Hong Kong, Ireland, Netherlands, Poland, Spain, Italy, Germany, Austria, Bahamas, Mexico, New Zealand, Singapore, Norway, Saudi arabia, United arab emirates, Bahrain, Croatia, Malaysia, Colombia, Panama, Jamaica, Barbados, Bangladesh, Bermuda, Brunei darussalam, Bolivia, Ecuador, Egypt, French guiana, Guernsey, Gibraltar, Guadeloupe, Iceland, Jersey, Jordan, Cambodia, Cayman islands, Liechtenstein, Sri lanka, Luxembourg, Monaco, Macao, Martinique, Maldives, Nicaragua, Oman, Peru, Pakistan, Paraguay, Reunion, Viet nam, Uruguay, Chile.