Crossbow limbs are a Members-only item, and are used to make crossbows. They can be smithed or obtained as a drop, but most can also purchased at the crossbow shops in Keldagrim, White Wolf Mountain, and The Dwarven Mines. The experience and Smithing (Crafting for Silvthril) level needed to make them are as follows:

Bronze612.5Bronze limbsUsed with a wooden stock at level 9 Fletching to make an unstrung bronze crossbow, granting 12 experience.
Blurite1317Blurite limbsUsed with an oak stock at level 24 Fletching to make an unstrung blurite crossbow, granting 32 experience.
Iron2325Iron limbsUsed with a willow stock at level 39 Fletching to make an unstrung iron crossbow, granting 44 experience.
Steel3637.5Steel limbsUsed with a teak stock at level 46 Fletching to make an unstrung steel crossbow, granting 54 experience.
Mithril5650Mithril limbsUsed with a maple stock at level 54 Fletching to make an unstrung mithril crossbow, granting 64 experience.
Adamant7672.5Adamantite limbsUsed with a mahogany stock at level 62 Fletching to make an unstrung adamant crossbow, granting 82 experience.
Rune9175Runite limbsUsed with a yew stock at level 69 Fletching to make an unstrung rune crossbow, granting 100 experience.
Dragon94100Dragon limbsUsed with a magic stock at level 94 Fletching to make a Dragon c'bow (u), granting 100 experience.
Silvthril7050Silvthril limbsUsed with a blisterwood stock at level 70 Fletching to make a Blisterwood stake-thrower crossbow (u), granting 50 experience.
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