Spiders, either in wire or brass, are used as a central hanging point for a lampshade. Choose one with the right number of legs to suit your lampshade. Normally if your lampshade was constructed with a crown it would be fitted inside with a spider.
Spiders are attached to the shade by trimming each leg to about 25mm longer than the radius of the top of the shade and bending the legs to match the angle of the top side panels. Then tin the legs and solder them into the inside seams.