As with the Basic ranking in all fantasy novels. This also follows the F-A ranking with A being the highest rank. There are other ranks above A such as the S-SSS ranks.
* S: This is a powerful item that is capable of unleashing great power but most of them come with conditions or time limits
* SS: Same as S but slightly stronger and comes with lesser conditions
*. SSS: Most SSS rank items possess no restrictions and incredibly powerful effects. Example: Soldier Uniform
Above that we have the following ranks:
* Disaster-Rank: Items that may as well be classified as acts of God, with immediate and extremely powerful effect. Example: Hestia's Guns
*Supreme-Rank: Items of unlimited power, their effects are immediate and are truly acts of God. Their power can not be surpassed by any other unless it's a design oversight. Example: Kingsley's Lord Clothing
However please note that because a person has an item of a higher rank doesn't mean that they automatically win the battle. it still comes down to the user.
Note: Despite the fact that the Guns are disaster class weapons, it doesn't mean that they can penetrate everything. an s-rank creature with a strong defense will block the bullets however defending itself against a continuous assault from said bullets is a different case