Coughtrie SW6 Lantern Installations
Coughtrie's SW6 Wellglass fitting was likely for up to 60W GLS lamps. They were incredibly simple in design, with a small aluminium-alloy body, with a glass support ring. The fittings were very small, having no room for anything but the lamp. It appears to have been succeeded by the Coughtrie SW10 for up to 100W GLS lamps, so nowadays it is no-longer on the market.
Loughborough
A great comparison between the SW6 and SW10 can be found at The Great Central Railway, Loughborough. Mounted to the side of a café building are both of these lights.
The original screws are long-gone, perhaps due to the threads wearing out inside the lantern's body, so new screws with nuts on the top of the canopy were employed to take their place. Nowadays, it has, installed, a domestic LED GLS lamp.