System and method for reduced thread stress for buttress style threads used in frac pump fluid ends

A fluid end for a reciprocating pump assembly, the fluid end comprising:

• a fluid end body defining an access opening having access opening threads formed on an inner surface thereof and extending between an inner threaded portion and an outer threaded portion;
• a blunt start formed at the outer threaded portion of the access opening threads;
• and
• a retainer nut having retainer nut threads formed on an outer surface of the retainer nut and extending from a first threaded portion to a second threaded portion, wherein to install the retainer nut in the fluid end, the first threaded portion of the retainer nut threads is configured to engage with the access opening threads before the second threaded portion of the retainer nut threads;
• and
• wherein, when the retainer nut is in a fully engaged position in the access opening, the second threaded portion of the retainer nut threads is offset from the blunt start of the access opening threads to define a circumferential offset distance therebetween.