Ed, I can't imagine relay contact wear was any kind of a major issue. I mean these cards are still around 40+ years later, many of them never refurbished still happily chugging along. I don't doubt your word, you still actually service this stuff in the field, which gets more use than my hobby stuff. I can't imagine there's ever much current being switched by those relays. The reason I don't like my H cards is they don't reliably go on hold. I forget what the rigamarole was, you had to be off hook for so long and had to hold the hold key a certain length of time, or whatever it was, but I just plain didn't like them. What I am more curious about is the difference between issue numbers on the 400D series cards. Seems like most of the other cards only had a few, but the 400D's had upwards of 15. I'm sure some of it is like Ralph said, a component change or something, but I'm wondering if there was ever a fairly significant change to the way the card worked. I use issue 15 as an example, the change allowed it to work on bridged ringing.