As the first finger of human hand, it is the most independent finger. The thumb is connected with inner heart of a person. Wearing ring on this finger on left hand indicates that you like to impose your will on others. Whatever, it will help boost your willpower. And you can wear it on the other thumb to show your ability to submit others' will. But please be attentive to any changes that occur in the time if you are wearing a ring on this finger. Perfect stones for thumb are ruby and garnet.