Will be purchasing some soon for the HWH system so I thought I'd ask. ;D
Hope everyone is having a great evening.
Napa or my local truck supply. Look online for a Gates catalog.
I like the old barrel and ferrule fittings. Our international and freightliner trucks have push locks and we chase leaks for ever.
I used brass fittings. Got some at the local hardware store, most at Amazon. I did get some push on fitting. Tried a push on check valve with some other parts at 100 psi in a bucket of water for a week. Lost 7 psi. I used then on the tank drain lines.
McMaster-Carr has DOT fitting in compression and push-in styles: McMaster-Carr (http://www.mcmaster.com/dot-tube-fittings)
You need to make sure that the fittings are DOT fittings. Regular ferule fittings from Ace are not DOT fittings.
I used brass fittings, ferrules and tubing inserts on all of the HWH side of things. I have a selection of push on fittings too, many from FT. All of the tubing is DOT nylon brake line tubing. I didn't do anything with the brake lines or fittings. Probably a good idea to use DOT approved fittings on any brake lines.
The McMaster-Carr DOT brass compression fittings appear to not have any tubing inserts. They are not significantly more expensive than high quality fittings from other sources.
You have to use DOT fittings on all air fittings as if a fitting fails it will affect your brakes.
I agree with Ron on tubing connections. HWH fittings are all Parker DOT fittings. But then on our coaches there are high pressure brass Tees and Crosses that do not have a DOT rating, check valves, nipples, water separators, step and slide cover valves and fittings, air cylinders that leak all the time. Use the best you can get. The DOT rating does not increase the price significantly.