This bracket is for a 6" Post to Beam because the bracket is 5" wide. The beam that it attaches to is a 2x so could be a 2x6" or a 2x8". Please see [this pdf](https://www.diyhomecenter.com/media/pdf/ozco-product-specs-51735-p2b-iw-6-post-to-beam.pdf) for details or feel free to call us at 800-666-9367 if you need any further assistance.