A lamp harp is the component of a lamp to which the lamp shade is attached. It typically comes in two separate parts, a saddle which is fastened under the lamp socket, and the harp itself which consist of a lightweight frame attached to the saddle at its lower end and extending upwards to a point above the bulb. At the top of the harp is a threaded rod. The shade's internal frame (known as a spider) mounts on this rod and is secured in place by a lamp finial. Common materials for harps include brass and nickel. The most common thread size is 1/4-27.
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Lamp harp Wikipedia(Text) CC BY-SA