Hammer union connections consist of male and female coupling halves secured by a threaded nut incorporating wing-shaped lugs that are struck with a hammer to tighten or loosen the connection. The seal sits in a groove on one coupling face, compressed when the nut draws the halves together, creating a metal-to-seal-to-metal sandwich that contains pressurized fluids. https://globalsealstech.com/product/hammer-union-seal-2/