inlet fitting 20 with the cavity and the communication of an exhaust port with the cavity as later described the diameter of the cap screw receiving holes 84 defined in the end plates and pump block are slightly greater than the diameter of the cap screws 70 wherein the clearance between the cap screw and the associated hole may constitute a passage for lubricating oil in the practice of the invention the lower left cap screw fig6 has an oil inlet metering spacer 86 inserted under the head thereof and this spacer includes a hole 88 fig7 which receives the cap screw and a metering passage 90 communicating with the hole and the lower edge of the spacer thus with the head of the associated cap screw 70 engaging the oil spacer 86 a passage under the cap screw head into the associated hole in end plate 72 is defined as will be noted in fig4 a groove 92 is formed in the end plate surface adjacent the cavity 82 and in communication with the cavity wherein lubricating oil entering the passage 90 may flow through the cap screw hole and groove to enter the pump cavity this flow path for lubricating oil insures adequate lubrication oil within the pumping chamber for lubricating and sealing.