Brass Knuckle Joint (Batten)
These are invariably used to connect a picture light shade to the stem.
10mm Threaded Entry Female
Diameter - 16mm
Height - 40mm
Plate Width - 17mm
Plate Length - 36mm
This joint works well with the top of picture lights, where the base is curved to fit the shade, and the other end 10mm female to connect with the extending arm.
Before starting any electrical work, always switch off at the mains. If in doubt consult a competent electrician