A friend has a very old house, and while exploring it found the following piece of cast iron hardware. It's about 2 1/2" across, has four holes with what seems to be set screws, and a fifth taller central hole. There are five mounting points that seem suited for flat head screws. The text "STANDARD" is written on it (split into "STAN" and "DARD"), along with the digit "7".
Any idea what it might be?
That is a ceiling light mounting plate, used with knob-and-tube wiring.
The flathead screws would fasten the plate to a ceiling joist, and the wires were fed through the larger holes. The center hole is intended to support the weight of the light, via another part that is missing from your example.
I think the setscrews held small insulators, probably ceramic or bakelite.
Two of the wire holes are opened, and the other two still have their knockout plugs in place. Four holes were needed only when continuing the wiring to another fixture.
Knob-and-tube wiring, and fixtures like these, are now obsolete and may not be legally installed in the U.S. Existing Knob-and-tube may be left in place, but not extended or modified. Any changes require complete replacement, which was probably done in your friend's house at some point.
