Usually, 5/16″ x 1-½ size sign bolts are considered perfect for mounting any signboard. It can mount a sign with ⅜ inches holes on the U-channel post and square post. You can use 2″ bolts for 1.12 lbs/ft u-channel posts and 2-½ inches for 2 lbs/ft. The bolts made from zinc are usually economical.