IF you are pouring cement from scratch, just mount the bracket in the (attached photo) to the base ground cement and this will fit. If I had known this, I would have done it this way, but someone else poured the cement. The other video shows the shim and a scrap piece of 3x3 post.IF you want to slide this over an existing standard 3x3 post, this is larger inside, so this might be sloppy.You could simply drive screws through the street side that touches the wooden post and that should work OK.(OR)….You could just screw this steel post directly to the street side of the wooden post, but…..You can make make a shim to make this fit better.3/4” plywood, 3-1/2” wide x *30” long.30” is my length.Your length might be different.The wooden posts are NOT 3x3.They are 3-3/8” x 3”.Put this shim on the street side or the rear side.Do not screw the shim to the sides or this post might rock back & forth.This metal post is 3-7/8 square.Screw these shims to your existing post, then slip this steel post over the wood post and check the fit. Don’t force it or it will get stuck. Then drive a bunch of screws into it.At this time, you can move it side to side to correct the angle if it is a little off (like mine was) then drive the screws in.This is the plan for my post. You might have a different setup. Hope this helps.
Anton Romanov 
