Source: Dungeon Master's Guide

Wondrous item, rarity varies (requires attunement)

While wearing this belt, your Strength score changes to a score granted by the belt. If your Strength is already equal to or greater than the belt's score, the item has no effect on you.

Six varieties of this belt exist, corresponding with and having rarity according to the six kinds of true giants. The Belt of Stone Giant Strength and the Belt of Frost Giant Strength look different, but they have the same effect.

Type Strength Rarity
Hill Giant 21 Rare
Stone/Frost Giant 23 Very Rare
Fire Giant 25 Very Rare
Cloud Giant 27 Legendary
Storm Giant 29 Legendary