Rigid Industries E Series Installation Instructions Manual page 7

Figure 9.1:
step 10
Place Rigid grille on shell and install (4) 1/4-20 x 5/8 Long SS Button Head Screws, (4)
1/4-20 SS Nyloc Nuts, (4) 1/4-20 SS Washers in the corners of the grille. See Figure 10.
Figure 10:
Figure 10.1: