Method for designing a nozzle module for a nozzle set for a spray gun, in particular a compressed air atomizing paint spray gun, comprising at least one nozzle module group (10, 20, 30, 40) having at least two, preferably at least four, different nozzle modules for selective attachment in or to the same base body module of a spray gun, wherein the nozzle modules are designed such that they have a different material throughput under the same spraying conditions, wherein the nozzle modules are designed such that the spray jets that can be produced by means of the nozzle modules have substantially the same spray jet cross-sectional height (h) and the same spray jet cross-sectional width (b), in particular the spray jet cross-sections of the various nozzle modules are congruent, characterized in that the method comprises at least the following steps: - determining at least one spray jet cross-sectional height (h) and/or one spray jet cross-sectional width (b) of a spray jet to be produced by the nozzle module, - constructing the nozzle module that produces a spray jet that has the specified spray jet cross-sectional height (h) and/or spray jet cross-sectional width (b), wherein the method comprises constructing an air cap (55, 155), wherein the construction of the air cap (55, 155) comprises adapting an outer horn air outflow angle (W1, W101) and/or an inner horn air outflow angle (W3, W103) and/or a control bore distance (Y7, Y9, Y107, Y109) to a material throughput and/or to an internal nozzle pressure of the nozzle module, wherein the outer horn air outflow angle (W1, W101) is the angle at which horn air flows out of an outer horn air opening (57a, 157a) of the air cap (55, 155) relative to a perpendicular axis, wherein the perpendicular axis is perpendicular to a central axis of the air cap (55, 155), wherein the inner horn air outflow angle (W3, W103) is the angle at which horn air flows out of an inner horn air outflow opening (59a, 159a) of the air cap (55, 155) relative to the perpendicular axis, and wherein the control bore distance (Y7, Y9, Y107, Y109) is the distance between at least one control bore (61, 63, 161, 163) in the air cap and a central opening (80, 180) in the air cap (55, 155). - determining at least one spray jet cross-sectional height (h) and/or one spray jet cross-sectional width (b) of a spray jet to be produced by the nozzle module, - constructing the nozzle module that produces a spray jet that has the specified spray jet cross-sectional height (h) and/or spray jet cross-sectional width (b), wherein the method comprises constructing an air cap (55, 155), wherein the construction of the air cap (55, 155) comprises adapting an outer horn air outflow angle (W1, W101) and/or an inner horn air outflow angle (W3, W103) and/or a control bore distance (Y7, Y9, Y107, Y109) to a material throughput and/or to an internal nozzle pressure of the nozzle module, wherein the outer horn air outflow angle (W1, W101) is the angle at which horn air flows out of an outer horn air opening (57a, 157a) of the air cap (55, 155) relative to a perpendicular axis, wherein the perpendicular axis is perpendicular to a central axis of the air cap (55, 155), wherein the inner horn air outflow angle (W3, W103) is the angle at which horn air flows out of an inner horn air outflow opening (59a, 159a) of the air cap (55, 155) relative to the perpendicular axis, and wherein the control bore distance (Y7, Y9, Y107, Y109) is the distance between at least one control bore (61, 63, 161, 163) in the air cap and a central opening (80, 180) in the air cap (55, 155).