I was talking about the BrakeQuip flare tool which I thought the question was asked about.
They do double flares so that is not an issue.

If looking at any other flare tool for brake lines then yes, be sure it'll double flare.

•1951 GMC 250 in the Project Journals
•1948 Chevrolet 6400 - Detroit Diesel 4-53T - Roadranger 10 speed overdrive - 4 wheel disc brakes
•1952 Chevrolet 3800 pickup
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"First, get a clear notion of what you desire to accomplish, and then in all probability you will succeed in doing it..." -Henry Maudslay-