These brackets are not actually 4x4 and 4x6" in size.  They are meant for a 'finished' 4x4 and 4x6 beam (its closer to 3.5x3.5 and 3.5x5.5)  If you buy an actual 4x6" beam (rough cut) it will not fit without serious modification.

Also unless you plan on burying the legs in the ground, do NOT get 4x4 posts that are longer than 8 feet.  I purchased 9 foot posts, based on the review that says they used 10 foot posts.  With 9 foot posts, the bottom of the cross beam is essentially 9 feet up in the air (I cannot touch it while standing on the ground, and Im 6'2").  There is nothing actually wrong with the brackets, but there is a lot of bad information related to this product on the wayfair site.