If it helps, the McMaster Carr catalog gives the max pressures for regular steel brake line as 6,000 psi for 3/16" and 4,500 psi for 1/4". I don't know if this is max working pressure with what factor of safety, or burst pressure, but it may get you in the ball park so to speak.

What are you planning to do?

Grigg

•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-