Nusa, It gets even more confusing if there is no RJ45 spec. For example, the RJ45S spec seems to include a physical key, so you can't use those dimensions. How is this tribal knowledge to be perpetuated once the wiki and connector mfgs change with the wind?
What makes you think the “wind” is changing? We moved to twisted-pair Ethernet in the early 90s, and there’s no evidence whatsoever of this changing any time soon.
tooki, There is no such thing as an RJ48C connector?
Nope. I don’t know any way to explain it other than what I’ve said already: RJ48C uses the 8P8C connector. But the 8P8C connector is NOT limited to RJ48C, so it’s not an “RJ48C connector”.
Sometimes nuance of language is irritating. Maybe it is a Port rather than a connector? It is labeled as "E1/T1 Test Port" and in the document it says RJ48C, but that is under a larger heading of all instrument connectors listing their type (USB, HDMI, PCIe, RJ48C, BNC, SMA, etc.).
I’d word it as “it’s an E1/T1 test port wired to the RJ48C standard”. “Port” indicating the function, and the “standard” defining the implementation, namely the connector and pinout.
It looks totally the same as the "RJ45" port you'd see for your laptop Ethernet, but that is not what it's for.
Yup, because, as we’ve said repeatedly, the 8P8C connector has many different uses.
I presume this square hole meets the combined requirements you've mentioned?
If it’s for a T1, it’s going to be RJ48C, if it’s for Ethernet, it’ll be T568B (or A). But since Ethernet is extremely consistent in using the T568B (and A) standard, saying it’s an [insert link speed here] Ethernet jack is sufficient to know what it actually means in practice.
Please, please, please, carefully read the “registered jack” wiki article I linked to earlier. I feel it explains all of your questions quite well, and we are all clearly going in circles.
There was a mistaken reference to RJ48C for the LAN port that instigated this.
So the device has both a T1 port and an Ethernet port? Then it probably explains the marketing intern’s confusion.

They saw the T1 port correctly labeled as conforming to RJ48C, and they mistakenly assumed this was the connector name, and so when they looked at the Ethernet port with the same connector type, they assumed it was also RJ48C, which it isn’t.