What's this outside box at my house?

[AL_as_needed]

Not sure if this should be its own topic or not, but seems to fit in with this one.

I am getting more into the wiring and network side of telephony out of necessity. The growing collection is soon to be in a new permanent home and I'm trying wire up my house to use more of said collection. Basic cabling and phone jacks I understand well, but bigger pieces of hardware are a mystery. First item needing clarification is this:

Basically what exactly is it and how does it work? I rescued it from a building that had a PBX in it at one point that was being cleared out.

[5415551212]

I call that a protector block those are required by the electrical code whenever a outside line enters a building. It protects from accidental contact with higher voltage power lines etc. The screws on the far left side might contain fuses also.
There is typically a #6 AWG copper ground wire that runs from that to the building electrical ground like a ground rod or metal water pipe.
The incoming lines land on the protector first before they continue to the PBX.
If your running phone lines between two buildings on private property you need something like that to comply with the electrical code.

[poplar1]

It's just a larger version of the 1- or 2-line interface installed today in residential or commercial applications. It connects the drop wire from the pole to your inside wiring. This one handles up to 6 lines, and usually has a 6-pair drop from the pole. It could be for lines (for single line phones or a multi line key system), or for up to 6 trunks for a PBX.

[5415551212]

Here are some links if your interested
http://bellsystempractices.org/400-/460-/460-100-400-i05_1978-03-01.pdf

https://vintage-phones.com/phonefiles/Bell%20System%20Practices%20000-000-000%20to%20%20500-000-000/462-005-100_I3.pdf

Here is a data sheets from a modern tyco gel filled one I typically encounter:
 https://globaltech-online.net/tyco/copper/Data%20Guard%20GSSP%20Station%20Protector.pdf

[AL_as_needed]

Thank you all for the insights!

I have an older (50s) Bell publication, I believe it is called "Station installation manual" but it did not mention larger outdoor equipment. I think I'll use this one like a punch-down block in my basement. That way I can either tie everything together or keep separate lines.

Im sure I'll have more questions and equipment pop up as the project gets going.