Please remember to properly support the copper-nickel line and do not allow anything loose to rub against it. It will chafe through in short order.
Also, if you are making your own flare it is also extremely important to "seat" the flare in the mating fitting. This usually requires multiple passes tightening and loosening the fitting nut.
And finally, professionals aren't likely to make simple mistakes like leaving the nut off the tubing. These guys are just trying to make themselves feel better. Professionals do things like put the nut on backward or worse, put the wrong nut on altogether!
