A hammer union includes a male sub, a threaded female sub, a threaded union nut disposed around abutting ends of the threaded female sub and the male sub, the abutting ends of the threaded female sub and the male sub include contact surfaces perpendicular to a longitudinal axis of the hammer union, and an outermost diameter of the perpendicular contact surfaces and a minor thread diameter of the female sub are equidistant from a longitudinal axis of the hammer union. A method of assembling a hammer union includes inserting a plurality of load segments between a threaded union nut and a male sub, threadedly engaging internal threads of the threaded union nut with external threads of a female sub, and engaging flat contact surfaces of abutting ends of the male sub and the female sub.