Ebay sellers and their surplus equipment sources, that separate/lose the connector blocks from I/O expansion plugins in equipment such as the HP 3488A Switch/control unit, HP 3497A data acquisition/control unit, etc.
These use plugins that consists of a card, and a plastic-body connector that attaches to the card and has the terminal blocks etc for cable connections. The two parts form a single part number, since each part is useless without the other. Usually the HP part number and description of the card label is on the plastic connector block part, since that's visible from the back of the machine.
Here's an example:
https://www.ebay.com/itm/254300899488 Seller has bins full of cards for the HP 3488A, all of them missing the connector blocks.
Here's a rare sight:
https://www.ebay.com/itm/224062686490One of those cards for sale WITH the connector block.
Quite often you see the mainframes being sold as 'unpopulated' but some idiot has just pulled off the connector blocks leaving some (or all) the actual interface cards in their slots. If you buy something like that you are getting a lot more for the $ than the seller knows. But then you have to find connector blocks.
Like this 3488A I just received. Contains one 44471A general purpose relay card, but missing the connector block.
There are always far fewer connector blocks on ebay than their mating cards. So what happens to the connectors?
With the HP 3497A/3852 the connector blocks are quite big and look like they might contain something other than just a connector. When unlocked and pulled from the back they come out quite easily, but the mating circuit board is much more difficult to extract. Deliberately. So seeing these connector blocks listed on ebay as if they were the complete card, is quite common.
Here's an example. Fool thinks he has a whole unit, but only has the connector:
https://www.ebay.com/itm/403461811989What the complete unit looks like:
https://www.ebay.com/itm/372738248549Anyway. Idiots. I hate them. I just wanna get some cards (with connectors) for my 3488A and idiots are making life difficult.
It's the same syndrome as people who leave the rack-mounting half of slide rails in racks. Morons.