The HPS Performance 5/8 (16mm) high temperature reinforced black silicone cap is designed specifically to be installed on your cooling system. Vacuum caps have no reinforcement and are intended for vacuum and very little pressure. The HPS reinforced silicone caps are manufactured just like our reinforced silicone radiator hoses. While traditional rubber coolant cap might crack and cause coolant leak, HPS Performance high temperature 3-ply polyester reinforced silicone caps will withstand the high temperatures and pressures of your cooling system for years to come.HPS Reinforced Silicone Caps are compatible for use with coolant, water, air, turbocharger bypass valve ports, vacuum ports, throttle body water ports, heater cores, and much more.Technical SpecificationProduct Type: Reinforced Silicone Coolant CapHPS Part Number: RSCC-062-BLKTemperature Range: - 65 deg. F to + 350 deg. F (177 deg. C) Reinforced Layer: 3-ply PolyesterInside Diameter: 5/8 (16mm) Color: BlackWall Thickness: 4mmInside Length: 1-3/16Overall Length: 1-5/8UV and ozone resistantRemark: HPS reinforced silicone caps are not compatible with fuel, oil, or any petroleum-based products.