DB, good find! Is this the dimension used on brake lines? Also, if I was asked to design a copper brake line, I would make the wall thickness larger (either by reducing the ID a bit, and/or by increasing the OD, preferably the 2nd). I am not sure though how this would be compatible with the fittings, but I think it would work. Point is though that lack of material strength can be compensated by thicker material. Also, I would probably specify a higher grade copper alloy, and I would try to achieve a design factor of at least 2. Problem is of course, as the pipe gets thicker/stronger material, it may get harder to bend. D^2 At 10:47 PM 6/2/2002 -0700, you wrote: >My handy dandy McMaster-Carr catalog tells me: > >5/16" OD Copper tubing Max Pressure 1197 PSI >5/16" OD 304 Stainless Max Pressure 3500 PSI > >Unfortunately, the type of steel tubing used on cars isn't listed, but the >type they do list (carbon steel) is about the same strength as 304 >Stainless. > >In service, I calculate that the peak pressure in a panic stop in the brake >lines of a disk brake car is somewhere in the range of 1200 PSI. > >Dick Benjamin