Full-root-radius-threaded wing nut having increased wall thickness

According to one aspect, a hammer union includes a female sub; a male sub; and a wing nut that is concentrically disposed about the female and male subs. The wing nut includes a body having first and second end surfaces, and an exterior surface extending therebetween; a passage extending through the body from the first to second end surface that defines an interior surface of the body; an internal shoulder formed by the interior surface; an internal threaded connection that extends from the first end surface and towards the internal shoulder; and lugs extending radially from the exterior surface. In one aspect, the body has a wall thickness defined between the interior and exterior surfaces, with a greater wall thickness at the internal shoulder than at the first end surface; the internal threaded connection has a full-root radius; and a lug that extends along the axial length of the body.