FIG. 1 is a perspective view of the front and the top of the support rail assembly;

FIG. 2 is a perspective view of the back and the bottom thereof;

FIG. 3 is a first side view thereof;

FIG. 4 is a front view thereof;

FIG. 5 is a back view thereof;

FIG. 6 is a second side view thereof;

FIG. 7 is a top view thereof;

FIG. 8 is a bottom view thereof;

FIG. 9 is a perspective view of the front and the top thereof, showing a shelf support and a shelf in position on the support rail assembly;

FIG. 10 is a perspective view of horizontal support member;

FIG. 11 is a perspective view of the back and the bottom thereof;

FIG. 12 is a first side view thereof;

FIG. 13 is a front view thereof;

FIG. 14 is a second side view thereof;

FIG. 15 is a back view thereof;

FIG. 16 is a top view thereof; and,

FIG. 17 is a bottom view thereof.

The broken lines in FIGS. 9 and 10-17 showing of environment are for illustrative purposes only and form no part of the claimed design.

The horizontal support member shown in FIGS. 10-17 is shown detached for clarity of illustration.

The ornamental design for a support rail assembly, as shown and described.