Mounting with two screws is important to prevent the plate from twisting, but note that most lens plates will require a 3/8"-16 to 1/4"-20 Reducer Bushing in the larger threaded insert. These are inexpensive, and it seems Canon could easily have included one in the box. Much better ...
Thinner Rain Automatic Gun Cleaner Headlight Renewal Coating Zero Voc Reducer BODY FILLER & FINISHING GLAZE 21 Key-Lite Lightweight Body Filler Premium Plus Body Filler Key-Flo 22 3M Body Filler And Glaze 3M Short Strand Body Filler 3M Blue Creme Hardener 23 Metal Bite Finishing Glaze Bumper ...
but note that most lens plates will require a3/8"-16 to 1/4"-20 Reducer Bushingin the larger threaded insert. These are inexpensive and it seems Canon could easily have included one in the box. Much better would have been to machine the needed Arca-Swiss dovetail grooves into the foot ...