The ornamental design for a stayrod for a high pressure oil field pump, as shown and described.
FIG. 1 is a perspective view of a high pressure oil field pump having an upper and a lower stay rod for a high pressure oil field pump mounted thereon, the high pressure oil field pump being shown in dotted lines as not forming a part of the presently claimed invention;
FIG. 2 is a front perspective view of a stay rod for a high pressure oil field pump of the invention, showing three of the fluted surfaces thereof, the remaining three fluted surfaces on the rear being mirror images thereof;
FIG. 3 is a top end view of the stay rod for a high pressure oil field pump of FIG. 2; and,
FIG. 4 is a bottom end view of the stay rod for a high pressure oil field pump of FIG. 2.