Crosshead and crosshead guide are made of ASTM A48-83 mechanized featuring god abrasion resistance and long service life. Besides F-500 mud pump that is cylindrical structure, upper and lower guide structures are sued for other mud pumps, so that the concentricity can be adjusted by adding space under the lower guide. Flange-bolts with pinhole fit are used for connecting crosshead to extension rod. This rigid connection ensures the concentricity of extension rod and crosshead. Coupling is used for connecting extension rod to crosshead. Light coupling enables the extension rod and the crosshead to connect to each other with ease and reliableness