J-B Weld™ Ultimate Copper Gasket Maker & Sealant is an RTV (Room Temperature Vulcanized) Silicone gasketing material designed for use in mechanical assemblies where high torque or closely spaced bolt profiles can lead to higher loads and cause gasket and sealing failures for average silicones. Curing occurs when the product is exposed to moisture in the air. The silicone then forms a tough, waterproof, gasket (seal) on most surfaces. It will not shrink or crack, resists oil and petroleum products, resists weathering, is sensor safe, and has good temperature resistance up to 700⁰ F intermittent. It's great for many automotive applications.