A piston rod for pumping paint includes an elongated cylindrical stem and a piston rod cap connected to the cylindrical stem. The cylindrical stem is formed from metal and has an outer diameter that is uniform along most or all of a length of the cylindrical stem. The piston rod cap is cylindrical and formed from metal. The piston rod cap includes an annular top portion that has an outer diameter that is larger than the outer diameter of the cylindrical stem, an annular bottom portion that has an outer diameter that is larger than the outer diameter of the cylindrical stem, and an exterior recess located between the annular top and bottom portions. The recess has an outer diameter that is smaller than the outer diameters of the annular top and bottom portions.