Is the top cradle area 3.5″ wide?
Yes. It is designed to receive a nominal 4″ x 4″ or 4″ x 6″ post or beam between the tangs. Larger sizes must be notched to fit. Make sure the post or beam is in full contact with the horizontal space between the tangs and not resting on the top of the tangs. You may chamber the edges of the notched area for ease of fit in between the tangs.