The ornamental design for a single balldownspoutjoint, as shown and described.
FIG. 1 is a bottom perspective view of our new design for a single ball downspout joint;
FIG. 2 is a front elevation view of our new design for a single ball downspout joint, wherein a rear elevation view is identical;
FIG. 3 is a left side elevation view of our new design for a single ball downspout joint, wherein a right side elevation view is identical;
FIG. 4 is a bottom plan view of our new design for a single ball downspout joint;
FIG. 5 is a top plan view of our new design for a single ball downspout joint;
FIG. 6 is a front perspective view of our single ball downspout articulated toward the front of the joint; and,
FIG. 7 is a front perspective view of our single ball downspout joint articulated toward the right side of the joint.
The broken line showing of the interior of the double ball downspout joint is included for the purpose of illustrating portions of the article and forms no part of the claimed design.