This small Wellglass fitting could accommodate 60W-200W GLS, or occasionally 80W-125W MBF/U. A few different designs were produced, including one with a wide-brim or a flush brim. These tiny things would be unable to house more than the lamp, so in the mercury versions, so the control gear would need to be hosted separately.

Crewe

It took a while to identify this Wellglass fitting, as I'd never seen one of these with a wide-brim before. Located at the end of Third Avenue, it's in a rather precarious position, hanging on by nothing but the wires!