You’re just talking about the airline to the horn, right?
A system will only flow as much as the smallest fitting will allow.
So if doing 5/8 or 3/4 DOT tubing, you want at least 1/2" NPT threads everywhere.
well yah just the line to the horn…so in my case that would be 4 push fittings that i would have to up in size cause of larger air line…but everything else is already 1/2 NPT. So i should be good…