??? who buys these by circumference? They are sold by capacity or diameter.
So - my recenly installed tongue jack is 7-1/8" circumference (5,000 Lb jack). I bought this larger size becasue that's what a new tongue wheel fork would fit. The only wheel forks they sold fit the big jack, not your smaller jack (as was my original jack, smaller - but we bent our jack and we bent thewheel fork).
I had to drill the bolt hole larger in the fork collar so that I could use the largest pin size possible.
I had to use a grinder to enlarge the lower hole in my tongue plates, the upper hole was ok. Tedious - but it worked - did this at our campsite!
Existing threaded mounting bolt holes were fine.
My newer stronger jack is harder to crank - grrrr.
My jack and wheel-fork were both from Camping World.
I upgraded my fork to use two ball bearing wheels.
What popup do you have? (If you add the make, model, and year to your signature line, it helps the rest of us have a better idea of what you are dealing with, at least for many issues.)
Is there any extra clearance around the jack "tube"? Have you checked etrailer, Amazon, trailer supply places? (We have a trailer supply store in town that has been a source for some things we've needed over the years. Of course, we live in a state with lots of trailers of all sorts.)
We just put an electric jack on our TT, and IIRC, there was some extra clearance in the space on the A-frame, now covered by the mounting plate, so I can't see it. It's been so long since we had to replace the tongue jack on our popup that I don't remember the details, especially since that time, we had the dealer's shop repair it,