J. P. Gilliver (John) wrote:

I remember back in the days of 25-way D connectors and the DIN 41612
family, there were three classes (I can't remember whether class 1 or 3
was best), which were mainly to do with how much gold plating was on the
pins, rather than mechanical type of wear. The cheapest - about 50p for
a D-25 - was "gold flashing", i. e. there was gold there, but really
only to protect the pins from corrosion in storage while they were
waiting to be assembled onto something and used; they were really
intended for things that were plugged in and left in place, and rated at
something like 3 to 5 insertions. Class 2 was IIRR about 0.5 to 1 micron
of gold, and intended for things like circuit cards that would be
replaced or moved around from time to time, and rated for a few tens of
insertions. The most expensive - about 5 pounds for a D-25 - were 5
microns gold, intended for things being reconnected often; I think they
were at a few hundred insertions.

(For D types, there was also whether the pins were "formed" - made out
of thin sheet brass, thus hollow [these worked better than you'd
expect!], or "turned".)

I don't _remember_ anything about the plastic housings having different
number-of-mating-cycles qualities.

It's where metal shells meet and provide "capture" that
counts. A D-series connector usually has a metallic "shield"
surface, which also doubles as a capture shell. With
a slightly turned edge so it doesn't snag perhaps.

Once two connector pieces are "docked", that takes
some of the side-wards play out of mating. Then, it's
a matter of how the pins and contact surfaces on the
mate interact, as to how long the contacts hold up
to repeated insertion. On some connectors, they use
a surface lubricant to increase cycle life. Some IDE
ribbons were using that on their pins, and you can
tell when the lube has left the scene, as the insertion
force increases. If the insertion force becomes too high,
that's when the pins on the male tend to get smushed
over at 90 degrees to the intended direction.

It was some older Dsub designs, where the brass pins
used to get "pushed backwards" into the shell, because
the pins weren't held very securely. Those were most
annoying. I haven't had anything like that happen in years.

Paul