Which fixing? 3x3 post to a wall

[Hitch]

I use a lot of thunderbolts, much better than the spit version in smaller sizes.

As mentioned, they are great, but only in decent concrete or hard brick.

Id go with the studding and resin system. You can get small tubes that fit in normal skeleton guns now i believe.
Don't drill right through into the cavity though, or you will need to put a plastic sleeve in to get a proper fix.

 

[matt]

I did exactly this. 3" posts fixed to a wall. I used screws with the head sunk quite deep in the timber. The masonry was slightly moist garage brick on one side and hard as nails 1930's industrial brick under 1930's render on the other.