Hard lines should never be connected to moving suspension or brake parts, as the movement will fatigue the brake line. A flexible hose must be used between the hard line and caliper. Many disc brake kits come with rubber flex hoses. While adequate, many performance oriented drivers prefer steel jacketed lines. Classic Tube's Stop Flex braided steel brake hose has a 5,000 psi rating, while regular rubber hoses usually rate around 1,500 psi. The braided stainless jacket prevents volumetric expansion, a major culprit in a spongy brake pedal. The very high burst pressure is a safety plus and it produces a firmer and more responsive brake pedal feel. A kit for a '65 Mustang consisting of three hoses costs $119.85.