Adamant crossbow limbs are one of the components used to make an adamant crossbow. They can be smithed from an adamant bar at level 76 Smithing, granting 62.5 experience.
If making an adamant crossbow, the profit/loss will be roughly 11,736. If making an offhand adamant crossbow, the profit/loss will be roughly 7,867. This does not include the cost of stock or string.