These are the seven principle djinn rings which are handcrafted, consecrated, engraved and imbued their power into these with  their sigils of obedience, these are their right crystals used to host and contain these entities. This will make it easy for the summoner to perform their summoning ritual,  these rings will help the summoner to channel the respective strengths and powers of the djinn of you choice directly to you. Now this is the interesting part you will not only be able to get the power of one principle djinn but also those beneath him in ranks and command which will give you unlimited power and wishes, here you will be able to do anything that you've ever dreamed of. Any of these rulers can grant their summoner anything he or she may desire.