The six essential tools appear in a ninja manual known as the Shoninki, written by Natori Masazumi around the year 1581. A translation of the Shoninki is available in a book titled, "True Path of the Ninja" by Antony Cummins and Yoshie Minami.
The six tools are: 1. Amigasa (straw hat), 2. Kaginawa (hook rope), 3. Sekihitsu (stone pencil), 4. Kusuri (field medicine), 5. Sanjaku Tenugui (3 foot cloth), and 6. Tsuketake (fire starter), or donohi (body warmer). Hooks made by Iga Tengu