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The article discusses the common shortcomings of contemporary standardized automotive brake tubing connectors (tube joints) against the modern requirements. These shortcomings are originated in the inborn disadvantages of currently utilized cone-to-cone sealing surfaces' mating. During last decade modern production excellence mindset and lean manufacturing practice have developed additional requirements to the tube joints, with the focus on their assembly process. Correspondingly, at least 99.9% probability to assemble and seal each connector from the very first attempt at the designated assembly station is necessary to resolve the challenge. The article deliberates that 99.9% probability as the design target in pursuing connectors' excellence. The article also discusses the pathway to the connectors' design perfection via replacement of the existing cone-to-cone mating type between the sealing surfaces with a sphere-to-cone one.

Recently invented solutions (Canadian Patent 2593305 and United States Patent Applications 20090015008 and 20070194567) incorporate sphere-to-cone type of the interaction between sealing surfaces in a brake tube connector. An interaction of sphere-to-cone type has numerous advantages over one with a cone-to-cone type which is currently utilized in conventional automotive brake tube connectors. Incorporation of a sphere-to-cone interaction between the sealing surfaces dramatically improves connector's sealing robustness. Sphere-to-cone based connectors are resilient to the tube and seat axes misalignment. Correspondingly, sphere-to-cone based connectors have less variation of the securing torque and virtually no propensity to locked misalignment occurrence. The article analyzes another fundamental advantage of a sphere-to-cone mating over the conventional cone-to-cone one.

There currently are only two industry wide utilized designs of standardized threaded connector for brake tubing. The ISO design incorporates a “bubble” style of tube's end-form while the JASO/SAE design includes double inverted “funnel” tube's flare. Both designs are based on the arrangement of two conical (frustum) surfaces which have to be pressed against each other in order to provide sealing. Seal integrity robustness of those standardized connectors is not sufficient as some retorquing is usually required in the course of the assembly process in order to seal a number of them. Accordingly each plant must allocate resources for the associated detection and rework process as they strive for zero leaks in the field. Numerous investigations and root cause analyses reveal some fundamental shortcomings in their sealing capability. In order to achieve sealed state of the connector some self-adjustment and certain degree of sustained deformation of its components is expected.