Special accessories that are worn in the cape slot of the equipment menu which allows characters upgraded movements as well as additional bonus that could range from critical protection to other elemental protection.
The difference of the 3 grades are subject to success of the combination. Remember that the level of the grade will determine the success of producing a jetpack and there are no changes on the stat of the jetpack regardless of what grade you use.
Maybe upgraded with the same talic which is also used for creating it and the number of slots per jetpack is not predetermined.
The Anxious Gamer 