counterbore 50 this effectively extends the length of the combined volume plunger 3 and plunger extension 11 allowing outer end 52 of plunger extension 11 to extend from longitudinal bore 28 and from plunger retainer 9 as should be understood as actuating lever 5 starts to move toward handle 8 push block 4 forces both pressure plunger 2 and volume plunger 3 toward output body 6 across compression chamber 45 this movement causes volume plunger 3 combined with pressure plunger 2 to force a large volume of grease at low pressure past output check ball 20 against output spring 15 after actuating lever 5 has been fully rotated into abutment on handle 8 as shown in fig5 volume plunger 3 as well as pressure plunger 2 have traversed compression chamber 45 toward output duct 51 causing low pressure grease to pass along output duct 51 and pass output check ball 20 of output body 6 fig6 8 illustrate the adjusted position of grease gun 26 in which plunger extension 11 is mounted to volume plunger 3 midway into counterbore 50 thereof by selective rotation of plunger extension 11 by manipulation of thumb wheel 48 inner end 34 may be moved into an intermediate position along counterbore 50 of volume plunger 3 in this position grease gun 26 is capable of delivering grease at high pressure or at high volume depending on the extent of retraction of the actuating lever 5 specifically in fig6 actuating lever 5 is shown fully retracted such that grease gun 26.