Hi!  The came off a boat I had to scrap.  Two have about 1/2" thick 3"x5" UHMW backing plates and two have round spacers about 1/4" thick (from the factory).  Note that only 1 has the cover.  These do require two extra 1/4" holes to keep the bracket from twisting.  Mounts with about a 1.25" hole.  Thanks for looking and please examine photos and condition notes carefully to ensure this is what you want.  Also, please contact me if you have any questions.