KingStar wheel cylinders are factory tested with a pressure of 45 psi of dry air to ensure unmatched robustness. The test checks for porosity, leaks, presence, position and quality of cups, surface finish of bores and bleeder seal. All castings meet S.A.E. J431 Standards, and bleeder screws are case hardened for long, reliable life. Brake cups meet S.A.E. Standard J1601. Durable boots are made from premium EPDM rubber, meeting S.A.E. Standar J1604. KingStar wheel cylinders have been the reference accross North America for over 40 years.