40-325RXA ultra large size rod pump with a diameter of 82.55 is suitable for oil wells with 4-1/2 "tubing and high displacement suction. In the API specification, there is no such large-size rod type oil pump, but we have developed this large-size rod type oil pump based on actual usage needs and achieved good results in practical applications. The structural form of the pump includes a thick walled cylinder top mechanical fixed RXAM, a thick walled cylinder top leather bowl fixed RXAC, and a thick walled cylinder top mechanical+leather bowl top fixed RXAM-AC. The RXAM-AC structure is beneficial for improving the reliability of installation and operation. The pump barrel is an integral thick walled cylinder made of carbon steel or alloy steel chrome plated, carbon steel or alloy steel carbonitrided. The plunger can be provided with integral spray welded metal or chrome plated plunger. The valve cover can be provided with alloy hard gasket or rubber gasket valve cover. The valve ball and seat can be provided with hard alloy, cobalt alloy, stainless steel, zirconia, silicon nitride ceramic and other materials. Other attachments can be provided in carbon steel, alloy steel, and stainless steel.