Abstract: A fluid end includes a housing having a bore extending toward a cavity and a wear sleeve positioned within the bore. The fluid end also includes a plunger positioned within a plunger bore extending through the wear sleeve, the plunger reciprocating within the plunger bore. The fluid end further includes a wear sleeve retainer coupled to the housing and positioned to block axial movement of the wear sleeve, the wear sleeve retainer having external threads along a body that engage internal threads formed in the housing. The fluid end also includes an anti-rotation system, coupled to the housing, the anti-rotation system engaging the wear sleeve retainer to block rotation of the wear sleeve retainer in at least one direction. The fluid end further includes a packing nut coupled to the wear sleeve retainer.