I have decided to cut square dowel for the hangers off the arch that supports the decking after seeing a Chinese bridge which has them, save some money and have the timber, just have to cut the pine up into 12mm by 19mm, not square, will make it easier in fitting square dowel to the arch in stead of round.
Will cut square dowel on Friday going to be fun, use the circular saw to do the first cut and jig saw for the next, I plan to only have the rail deck up with a third bridge pier only temporary till the arch is built.
Tony from down under