The Spare construct arm (u) is used in the magical construct puzzle room in Daemonheim. It must first be imbued into a spare construct arm, which is then used to repair the magical construct. The magical construct will then open all the rune-covered doors in the room. If you imbue it wrongly (higher chances of success depend on your Runecrafting and Magic levels - higher levels having higher chances of success and lower levels having lower chances of success, provided you meet the required level in the first place), you will be dealt massive damage.
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