We at Hovr Strong Solutions prefer to use 5/16 - #18 set screws. You can, however, use smaller ones, such as ¼” - 20 or # 10 – 24.
We use a Cup point, Hex drive, Black Oxide, Alloy steel. All sizes are feasible as long as the tip will hit the center of the bottom of the male bracket when inserted completely, which is attached to the wall.
For the Steel bracket, we tend to use ½” long set screws. Not recommended for the aluminum bracket.