Can anyone recognise how to use this Junction Box

I collect old Electrical Fittings and I recently acquired this vintage Junction Box (photos attached). I've been trying to figure out how it would have been wired in/used.

This Bakelite Junction Box has a Depth of 1¼ inches with an outside Diameter of 2½ inches.

Viewed from the Top there are 4 brass Terminals labelled 1, 2, E, & LOOP. The upper edge of the Box forms a recess into which fits a 1/32nd of inch thick Cover Plate with a centrally positioned Rubber Grommet which has a ¾ inch diameter hole. Two cut-outs on opposite sides of the Cover locate in the Box Rim over two lugs and fixing holes (3/16th inch diameter) to provide a fit within the Rim of the Box.

There are two threaded brass holes (circa 3/16th inch diameter) at right angles to the fixing holes (one through the Earth Terminal and the other one independent) – unsure of the purpose of these holes.

Viewed from the underside there are two six sided Nuts which secure the 1 and 2 Terminals on the upper side. The Earth Terminal is replicated including both threaded holes. The fixing holes are enlarged to ⅜ inch diameter for a depth of ½ inch.

Any information thankfully received.

It would have been screwed to a round conduit junction.
the side with loop written on it would have been towards the conduit.
for lighting, live and switch wires would be terminated to the box before it was screwed to the conduit junction.

this would leave just 3 terminals L, N, E for the outgoing flex (through the baculite hole with rubber grommet) that would feed a light fitting.

Hi James, Your explanation is first class, thank you - I just could not figure it out but now I understand.

Round here, there are a lot of 1960's houses that were wired with these junction boxes for the lighting, using twin & earth into the top, and the pendant connections out to the bottom. The box is screwed to the underside of a timber noggin between joists (often a piece of old floorboard) with a hole for the twin & earth cables to enter.

There is no conduit.

The nogin is positioned so that the bottom edge of the junction box is either flush with the plasterboard, or slightly recessed.

Hi SJD,
Thanks for your explanation. I am trying to imagine the set up you describe and I will draw a diagram for myself to try to see it better.