This bracket fits snuggly on 4x4 post which actually measure 3.5" x 3.5".   Construction is .25" thick high quality aluminum with full weld coverage over joints.   There are a total of 8 holes to secure the post on all sides.   In addition to the bracket, you get the following
 
8x 2" Stainless Steel Wood Screws
8x Plastic washers
8x Screw caps
 
Necessary but not included:
Mounting hardware.   This will vary depending on your mounting surface.    Contact us for recommendations.