Assembled piston for engine

Claim 1

An assembled engine piston comprising a metal body member having an axially extending annular recess at the top end thereof, said recess extending to a top surface of said body, a ceramic material head member on the top of said body, said head comprising an axially extending annular projection extending into said recess, radially extending interengaging means within said recess and on said projection and said body for securing said head to said body against relative axial movement in response to rotation of said head with respect to said body, said interengaging means comprising at least two rows of threads of conical section on said projection, and threads on said body, said rows of threads comprising an upper thread and a lower thread, said lower thread of said projection having an inclined lower surface engaged by a correspondingly inclined lower surface of a body thread, and said upper thread having an inclined upper surface engaged by a correspondingly inclined upper surface of a body thread, so that the threads of said body exert forces on the threads of said projection which tend to compress the portion of the projection between said upper and lower threads, and means to prevent relative rotation of said head and body.