There's not enough pressure there to need a flare fitting, and steel line needs to be double-flared or it splits. Your local big box hardware store like Lowe's or Home Depot will have the compression to pipe fittings, and any auto parts store will stock several lengths of steel line. Don't overthink this.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!