Hmmm, I wondered about that also. Mine is a T1350 and I believe mine, too, has the 2 5/16. Yet I'm using a 2" ball. I never had any problem but did notice it a bit sloppy. The safety catch is enough to hold it but. I never saw any stamp on the tongue and I have no manual but I'm sure you guys would know best.
While I'm on this topic, last fall after the season came to a close I bought a 4" drop draw-bar.
You guys might remember an issue I complained about last year when my tongue was sitting too high and my TT had a sway after a certain speed. I had my TT spring re-arched hoping to raise the TT. I think I was targeting to the wrong theory. I didn't need to raise the TT but to lower the tongue.
With that, every time I pulled the TT off the end of our driveway or parking lots, the rear skid pieces always scrapped bottom with that annoying noise. I also found out later that the Ford Explorer has a higher rear receiver than most other tow vehicles. I'll know better this summer "to be continued"
Jerry & Debbie
Ford Explorer 4.6 Triton V8, AWD, 4x4
1985 Sunline Saturn T-1350
Ham radio VE3JCJ, VHF, UHF and HF