Modular system for producing a screw spindle pump comprising a housing, and a drive spindle which is accommodated therein, and one, two or more running spindles which mesh with said drive spindle, comprising: - a plurality of housing components - - comprising a housing base component which has a fluid inlet and which serves for forming a base pump chamber, - - a housing pressure component which has a fluid outlet and by way of which the drive spindle is mounted and which serves for forming a pressure chamber, - - a housing cover which is arrangeable on the housing base component and which serves for supporting one, both or all the running spindles, - - and identical housing intermediate components , any number of which are arrangeable between the housing base component and the housing pressure component and which in each case form an additional pump chamber, - - wherein the base pump chamber and one or more additional pump chambers complement one another to form a common pump chamber, - a plurality of running-spindle elements - - comprising one, two or more running-spindle base elements which are arrangeable in the housing base component , - - and identical running-spindle extension elements which are arrangeable in the housing intermediate components , - - wherein a running-spindle base element and one or more running-spindle extension elements complement one another to form a running spindle which is arrangeable in the pump chamber. - a plurality of housing components - - comprising a housing base component which has a fluid inlet and which serves for forming a base pump chamber, - - a housing pressure component which has a fluid outlet and by way of which the drive spindle is mounted and which serves for forming a pressure chamber, - - a housing cover which is arrangeable on the housing base component and which serves for supporting one, both or all the running spindles, - - and identical housing intermediate components , any number of which are arrangeable between the housing base component and the housing pressure component and which in each case form an additional pump chamber, - - wherein the base pump chamber and one or more additional pump chambers complement one another to form a common pump chamber, - - comprising a housing base component which has a fluid inlet and which serves for forming a base pump chamber, - - a housing pressure component which has a fluid outlet and by way of which the drive spindle is mounted and which serves for forming a pressure chamber, - - a housing cover which is arrangeable on the housing base component and which serves for supporting one, both or all the running spindles, - - and identical housing intermediate components , any number of which are arrangeable between the housing base component and the housing pressure component and which in each case form an additional pump chamber, - - wherein the base pump chamber and one or more additional pump chambers complement one another to form a common pump chamber, - a plurality of running-spindle elements - - comprising one, two or more running-spindle base elements which are arrangeable in the housing base component , - - and identical running-spindle extension elements which are arrangeable in the housing intermediate components , - - wherein a running-spindle base element and one or more running-spindle extension elements complement one another to form a running spindle which is arrangeable in the pump chamber. - - comprising one, two or more running-spindle base elements which are arrangeable in the housing base component , - - and identical running-spindle extension elements which are arrangeable in the housing intermediate components , - - wherein a running-spindle base element and one or more running-spindle extension elements complement one another to form a running spindle which is arrangeable in the pump chamber. <EOS>