Brass Knuckle Joint (Batten) 10mm Male and 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