Abstract: A Removable Thumb Turn Attachment is disclosed. The device and system incorporate a thumb turn cap that is attachable to the head of a conventional deadbolt key. The system may include a retaining cap assembly that is installable over a conventional deadbolt lockset. The retaining cap assembly cooperates with the thumb turn cap so that the thumb turn cap will engage the retaining cap assembly so that the thumb turn cap, once inserted, cannot be readily removed from the retaining cap assembly. The thumb turn cap and retaining cap are installable on a conventional key-operated deadbolt lockset so that the lockset is converted to operate as a thumb-turn-operated deadbolt lockset.