The ornamental design for a belt-mounted tool holder, as shown and described.
FIG. 1 is a front view of the belt-mounted tool holder embodying my new design,
FIG. 2 is a rear view of the tool holder,
FIG. 3 is a left side view of the tool holder,
FIG. 4 is a right side view of the tool holder,
FIG. 5 is a top view of the tool holder,
FIG. 6 is a bottom view of the tool holder,
FIG. 7 is a front perspective view of the tool holder; and,
FIG. 8 is a front view of the tool holder with phantom lines indicating the tool holder on a belt, indicating the environment upon which the tool holder is used, the belt not being included as part of the disclosed invention.