2 Lucky--
There is definitely some confusion on the actual dimension of this bolt-on roller unit.
In your earlier post with the link to the E-trailer site for this item, you referenced the Ultra-Fab product UF48-979017. Both on the E-trailer site AND the Ultra-Fab website, the UF48-979017 is listed to fit a 2 1/2" crossbar. As a matter of fact, the Ultra-Fab website only lists two roller kits of this specific design--the 979017 fits a 2 1/2" bar and the 979018 fits a 3" bar. There is no listing for a 2 1/4" bar.
A search on the UF48-979017 part number brings up several different vendor sales advertisements for it---some of those ads do reference fitting 2 1/4" square tubing, and some reference 2 1/2". The set Ron purchased on eBay plainly says for 2 1/4" bars in his photo. However, on today's listing for UF48-979017 on Amazon I saw one question and one comment referencing the need to insert a spacer on the 2 1/4" bars to shim out since the kit is designed for 2 1/2" bars.
Finally, my crossbar on my 2019 2552 is 2 1/2" (double-checked), and has this unit installed. Since current descriptions for UF48-979017 on E-trailer, Amazon, and Ultra-Fab sites currently specify 2 1/2", and Ultra-Fab doesn't even currently list a 2 1/4" unit, I think you would safely receive one that will fit your hitch if you order from one of these sites. This is definitely something that bears careful scrutiny from anyone interested in this modification, however.
Mike