Supporting a large glass shade or lantern?  These lampholders used with chain provide a simple solution, which takes all strain off the electrical cable.  Available in a wide range of finishes you can match up exactly with both chains and ceiling hooks

This lampholder is great for use when suspending a heavy glass shade. Using shade locking rings to secure the shade, the hook connects to suspension chain from the ceiling, which takes the weight with no strain on the electrical connections.  This lampholder enables you to get creative with big shade options.

Weight loading shouldn't exceed 8kg. Shade locking rings are sold separately.   If in doubt consult a qualified electrician.