We claim the ornamental design for side rails of a treadmill, as shown and described.
FIG. 1 is a side, front perspective view of side rails of a treadmill;
FIG. 2 is a first side view of the side rails of a treadmill of FIG. 1;
FIG. 3 is a second side view of the side rails of a treadmill of FIG. 1;
FIG. 4 is a front view of the side rails of a treadmill of FIG. 1;
FIG. 5 is a rear view of the side rails of a treadmill of FIG. 1; and,
FIG. 6 is a top view of the side rails of a treadmill of FIG. 1.
The ornamental design that is claimed is shown in solid lines in the drawings. The broken (dashed) lines shown in the figures are included for the purpose of illustrating environmental elements only and form no part of the claimed design. The broken lines located on the top surface of the side rails delineating elongated strips are provide for the purpose of depicting features of the side rails that form no part of the claimed design.