Pump rods ( sucker rod)

7/16 or 3/8 inch are normally used. They should be replaced if worn excessively, and couplings are subject to significant wear. The critical area is around well pipe couplings, the rod couplings must not have interference , this is controlled by the length of rod protruding from cylinder, and distance cylinder pulled off bottom when coupling rod to mill pump rod ( which must be all the way down). On first stroke verify well pipe not pulled up.