Distributing Protection Cords
The protection cord is a string of three red coloured threads ....[with] three knots representing the nature of vajra body, speech and mind and blessed by their mantras and meditation. Therefore, the cord has power to protect disciples from obstacles. It should be tied around either of the disciples’ upper arms, while the master recites the mantra.
Text from: A Guide to the Kalachakra Empowerment by Kalsang Yeshi