A pressure-tight stein cylinder seal and a self-energizing stein shoulder seal matching the stein cylinder seal that both use an equilaterally triangular soft ring as their sealing element, wherein their designing rules are first, by means of wedging function of a hard gland coaxial with the stein cylinder, to convert their original axial tightening force 2f respectively into a radial compression force 4f/√3 of their soft ring 04 on the stein 02 cylinder and another radial compression force 2f of their soft ring 06 on the stein 02 shoulder and ensure that the two soft rings are so compressed from a great room to a small room as to be able to pass a pressure or stress exactly to each different direction, then to cut off their off-stein corners to give their cavities an opening or give each soft ring an axial compressing allowance, and last, by means of anti-extrusion metallic C-rings without axial resistance, to close each opening to provide a full support for the sealing deformation of their soft rings compressed in their cavities.