They can be for coax. We used them for power. They were used on a wafer-processing system that had stations such as spinners and ovens, connected by an air track the moved the waafers along. Power soucle come up from the power supply through those DB-size connectors and then be distributed on the module as needed.
Martin - I think I had you wrong on that connector, I thought the round things were Coax connectors - I have seen that before. But coincidentally, I came across that exact connector (the female one though) in an ethernet switch that used it as an external power connector. The large pins (sockets in my case) were used for the 3.3v, which on the internal power supply was rated at 30A. Pretty beefy.
@MeasurementBlues... Seems that this confusion came from the IBM-PC realm - from the users, I think. In the begining, all PCs used to have a couple of DB-25 EIA-232 standard (sort of) as default. So everybody learned to refer to it as a "serial DB-25 connector" (or port), Delta mini-sub or DB for short.
After a few years, with the arrival of Winmodem (USRobotics) and similar internal types all those EIA modem standard signals became useless. So someone decided to simplify the serial connection (make it cheaper), using an smaller mini-sub 9 pin connector in place of the bulk 25 pin model.
Suddenly, the DB-25 became "DB-9" due to a simple layman analogy. Some popular definitions simply stick and very often is not an easy task to trace back how it has begun.
Here in Brazil, people call UPS as "No-Break" - don't ask for an UPS on the specialized stores, as people will stare at you completely clueless. That is interesting once both (the term and the acronym) are from English that most people don't understand here...
@MB - them's the ones! They are a very versatile series of connectors - you can send a fair bit of power thru those pins, and with the option of COAX as well, what more could you ask? But they are too thick to fit on tablets and phones, and USB has taken over serial now, so I think they will get rarer and rarer.
@Andrewier...."despite my limited English abilities." Please don't apologise, if my command of other languages (French and Afrikaans in my case) was as good as your English, I would be a happy man!
I've also seen D-subs with coax connectors in them as well as pins. Pretty rare though. And they are also confusing in what is male and what is female the shells have a different sense to the pins. I stick with Pins = male which seems right most of the time. Don't you hate it when you misinterpret the catalog and you end up with wrong parts????
@David Ashton... I am glad to be of help, despite my limited English abilities. From what I remember ITT Cannon and Amphenol used to have all sorts of D-Subs, 2 and 3 rows kinds with odd countings like 25, 31, 36, 37, 51 and so on. Also interesting to note that shell size grows in order A, B, C, D and suddenly shrinks to E, the smaller of all shells. I remember that was a heavy nightmare to understand the Cannon catalog in order to build a proper P/N for ordering. I used to buy it for geomagnetic sensors, requiring shells and everything else to be made of non magnetic alloys, as brass or aluminum. It was a real challenge requiring double checking (usually more than one person) to make shure we wouldn't buy very expensive wrong parts!