1) Do you have a trailer with a 5-way plug?
B) Do you have a vehicle with a 5-way socket?
III) If the answer is ‘no’ to both of the above, why are you even worrying about it? Just get the 4-way to 7-way adapter and get on with your trailering life...
Well, I wouldn’t say I’m “worrying about it” - just thought that if 5-pin flat was “the up and coming thing” or common in some uses, since I’ll likely be looking for another trailer by July or so, going with the combo for a few $ more might (might) be a good pre-emptive move. Much less the time to find one again later if the need was likely to arise. (The combo adapter is “saved for later” in my cart/account, but, stuff like this has a way of suddenly being out of stock, these days, if one goes back to it 2 months later.)
Easy enough to ask while chowing breakfast, do a couple chores, come back and now I have my answer. :-)
Summary: “Petty darn uncommon.”
Besides, I / we got all these great diagrams & useful discussion posted on the thread as a bonus!! ;-)
So, I went ahead and ordered the combo adaptor. I should be set for any eventuality.
...Except there are also not only the 6-pin rounds, but evidently 5-pin round plugs and sockets are used in this app as well.
Ah, well. My intent to "be prepared" only goes so far...