Astrological bangles were recommended by Paramhansa Yogananda and his guru Sri Yukteswar. They can strengthen your aura and deflect or mitigate negative karma.
They protect one from negative astrological influences and help one to stay in attunement with Yogananda's line of gurus. They are created using a specific formula given to Yogananda from his guru Sri Yukteswar and passed down through Swami Kriyananda. If you read chapter sixteen of Autobiography of a Yogi you will find more information about astrological bangles as described by Paramhansa Yogananda.
The bangles are made with pure gold, pure silver and pure copper. These pure elemental metals are formed into the bangle with heavy round wire which is twisted together in a spiral helix pattern. The cost of a bangle depends on the price of gold.
They can be worn directly above the elbow, above the bicep muscle or around the wrist. Paramhansa Yogananda has recommended that you wear your bangle on the upper arm above the elbow.