Old wiring

[Stwood_]

My guess was 50's also....

The receptacle was an Eagle brand, I've seen more failures on them than any other. The Bakelite gets brittle over time.

Ed

About a month ago I replaced one of those no ground ones in our bedroom. 3 of them actually.
The first one fell apart like yours did. I didn't catch the brand name.

[MarkSingleton]

Electrical receptacles just plain need to be replaced after they
have been in service for multiple decades. Especially if you find,
as I have, that the "contractor grade" (cheapo) ones are worn
to a frazzle. The "back stab" junkie ones.

Our place is thirty plus years old. Receptacles that get used over
and over just plain get worn out.

I don't even look at the cheapest ones anymore. I get the best I
can find. Peace of mind for the small difference in price. After
awhile working with them, you can tell the cheap ones vs the
better ones just by the weight.

[FS7]

It doesn't take much to break a receptacle. I had several broken ones in my house, which is less than four years old, simply from overtightening the receptacle to the box or the terminal screws to the receptacle. That an old house with K&T wiring has a few doesn't surprise me at all for any reason. It's probably gone through a ton of thermal cycles, especially in Michigan.

[EricU]

we have had a number of the original receptacles break, from the early '80s.  I really should replace some more of them, lots of them don't hold a plug well.