So I just had to get a new radiator, the problem is the one I ordered the port for the cooler line is 12m*1.25 and the inverted flare connector from the line is 1/4". I ordered a converter from metric to imperial. But would there be a way to find an equivalent size at a hardware store instead?

I don't want to have to redo the line or get new ones.

 

Highly unlikely. Even beyond unlikely, I would say.

Almost certainly wrong. Those are generally 5/16" IF. 5/16" has ½"-20 threads; that's regular ½" fine thread; you should be able to screw that size nut on the flare nut. ¼" IF nut threads are 7/16"-20 (also the regular fine thread) if memory serves.

IF is harder to adapt to/from anymore. Used to be among the most common; not so much these days. You might end up having to adapt it twice, like, metric to AN, then AN to IF. Most of those things on newer cars are those O-ring QCs, so that's what's easiest to get for applications like that. Doesn't do you much good though if you've got a 5/16" IF line in your hand.

M12 x 1.25 is a weird size. Very fine threads. 1.5 threads are FAR more common on fittings.

Go to the hardware store and buy a bolt in whichever of those 2 metric sizes you can find the easiest and cheeeeepest, and a ½" fine nut, and check the fit on everything, before buying anything. Those fittings can run up quite a tab if you don't get it right the first time.

 

I think I might just buy a correct radiator so I don't risk creating weak points with chained converters.

 

Still, it'd be A Good Idea to identify the fitting sizes.