The HPS Performance 1/4" high temperature reinforced black silicone cap is designed specifically to be installed onto your cooling system. Vacuum caps have no reinforcement and are intended for vacuum and very little pressure. HPS Performance Silicone Caps are reinforced with 3 layers of polyester webbing and will withstand the high temperatures and pressures of your cooling system for years to come. They are compatible for use with coolant, water, air, turbocharger bypass valve ports, vacuum ports, throttle body water ports, heater cores, and much more. Temperature range: - 65 deg. F to + 350 deg. F (177 deg. C). Reinforced layer: 3-ply polyester. Inside diameter: 1/4" (6.5mm). Color: black. Wall thickness: 4mm. Inside length: 1-3/16". Overall length: 1-1/2". UV and ozone resistant. Remark: HPS reinforced silicone caps are not compatible with fuel, oil, or any petroleum-based products.