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 (5, 7) 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.