The Chain Mail is a full suit of chain mail replaced part of Connor's Light Chain Mail Set (Chainmail Gloves) and Leather Boots(and pants). Connor was assured that chain mail suit would guard him during the fiercest of battles. Connor found the chain mail suit in the Witch's Tower. He took it as it offered better protection over his previous armor, and he left the old armor behind. He knew that some poor fellow's loss was his gain. He continued to wear the Light Chain Mail Breastplate with the Chain Mail Suit, but left his Chainmail Gloves and Leather Boots behind.
Also if Connor didn't bring the suit he found in the swamp to Underground Realm of the Gnomes, the Armor Seller Gnome in the Armor Shop would offer him a Chain Mail Suit for sale for only 150 gold coins and the trade-in of his used protective gear.