The ornamental design for a threadedcoupling for a water system, as shown and described.
FIG. 1 is top plan view of a threaded coupling for a water system of the present invention showing my new design;
FIG. 2 is a front elevational view thereof;
FIG. 3 is a side elevational view thereof;
FIG. 4 is a rear elevational view thereof;
FIG. 5 is a cross-sectional view taken at line 5-5 of FIG. 2; and,
FIG. 6 is a cross-sectional view thereof shown in a position of use within environmental subject matter.
The dash-dot-dot-dash broken lines shown in FIGS. 1-5 depict environment only that forms no part of the claim. The evenly dashed broken lines in FIG. 6 illustrate environmental subject matter that forms no part of the claim.