The outer mud guard (shown here for the passenger side) attaches to a bracket with screws. (The inside end of the bracket is bolted to the frame with a 5/16 bolt.)

The outer mud guard is attached to the inner fender via 3 screws (red circles, heads in the engine compartment) and a single screw into the firewall (yellow).

The inner mud guard screws to the outer guard (orange screws. Order: screw head, inner guard, outer guard). It fits under the firewall support member and is held with two additional screws (green). Two bolts (blue) hold the inner fender to the same support member. On my car, I put the fender on the outside of the member.