So I'm in need of a new water filter at my place so I went ahead and purchased a 3M Aquapure. After doing some research I found out that it requires 3/8" fittings which would make for a fairly easy installation assuming that my water valve accommodates said measurement (I stupidly assumed so).

I purchased all the fittings and adapters, set up the entire filter and then went to connect it underneath my sink. Much to my dismay, my valve has 7/16" fittings

I'm now stuck with an entire filter unit and not sure where to go from here. I have the following 3/8" x 3/8" x 3/8" T-fitting which would have worked had my water valve been 3/8":

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I would need something that would adapt this fitting to the 7/16" male end of the valve which I believe I found but the problem is, I can't find anything that will allow me to connect the 7/16" hose into the top of this T-fitting.

Also, the plumber who installed the old filter unit has a bizarre reducer fitted to the outlet hose leading to the filter faucet and I have no idea what the size is. Maybe 1/4"? If that's the case, I've found nothing that accommodates a 1/4" male to a 3/8" female connection (nothing lead-free at least).

Seeing as everything is open, I don't think I can return any of this. Some help would be appreciated on how to piece all of this together. Feel free to laugh at my stupidity in all of this.