I came across this set of connectors. All are labelled 3COM and go from some type of plug that I can't identify to an ethernet end. Two of them have female RJ15 sockets, one has a male RJ15 plug.

Presumably / obviously these were to interface from something to ethernet, but I don't have any other 3COM hardware so I'm not sure what.

I think these are approx. 20 years old, perhaps > 2002.

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Those are PCMCIA adapters. With laptops, a single PCMCIA card was narrower than Ethernet (or phone lines). You could get a 2 card thing (but I don't recall any from 3COM)

This image:

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shows an example of 2 card Xircom (which had RJ-45 direct input but meant you couldn't use any other PCMCIA cards) and the narrower 3COM with the port your connector would plug into.

Note that you could use 2 of them to make your laptop into a really really terrible router, but you also could use one of them plus some other PCMCIA card.

(And from my experience, 3COM used the same physical interface between card and adapters, but not all cards worked with all adapters which was super fun if someone mixed them up ... though that could have also been a driver or bent pin issue)

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  • I had totally forgotten about these things :) – Thomas Apr 14 at 13:10
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    Back when I used to do support, we use to call those type of connectors "pig tails". This was a common way to make external connections from PCMCIA cards as they didn't block access to the PCMCIA card in the slot above or below. The connectors were detachable so that the PCMCIA card could be removed from the device and placed in an anti-static case when not in use. Because of this, connectors were frequently separated from their cards, as connectors remained in laptop bags, and PCMCIA cards we left in laptops as they were lost or upgraded. – Rick Sarvas Apr 14 at 16:19
  • PCMCIA in this answer stands for, "People Can't Memorize Computer Industry Acronyms". :-) – Tardisrepairman Apr 16 at 12:34

These were designed for 3COM Megahertz networking PCMCIA cards (aka PC cards). These were add-on cards for laptops that didn't have internal network adapters. See bottom device on this picture on Wikimedia.

Some versions of these cards were equipped with a small pop-up female Ethernet connector (the original XJACK), which obviated the need for these dongles.

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A few things to add to existing answers:

As well as ethernet cards there were modem cards, and some with both modems and ethernet adaptors in one.

There were several similar but mutually-incompatible connectors, so mixing and matching from different cards could be problematic. For combination cards you may need to check the icons on the card and connector.

Some later models were Intel branded.

The same connectors with different pins populated where used as charge (and perhaps pre-USB data or modem) cables for some mobile phones.

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    Additionally, these were relatively expensive accessories, so if you lost one or damaged it, there was some not-small costs involved in sourcing the right replacement. And they were very easy to damage by attempting to connect the LAN port to the Modem port or opposite. – Criggie Apr 16 at 6:04

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