Can anyone help me with the actual wood sizes? (And bridge building advice.)?

I don't really know the names for the wood sizes I want to use. I know I need to use pressure treated wood for this outdoor bridge, and the bridge must be able to support 800lbs. If anyone wants to give some tips on building this bridge, by all means do.





First, what are thee following pieces of wood? How would I ask for them in a hardware store:





4 x 4 x 12





2 x 4





2 x 6


----------------





Now, I think I may also need a board 6 inches wide and 1 1/2 inch thick.





How can I answer these questions for myself?





Thank you.


Can anyone help me with the actual wood sizes? (And bridge building advice.)?
Remember that ';dimensional lumber'; in the US is a far cry from it's stated dimensions.





4 x 4 x 12


I assume 4'; x 4'; by 12', just ask for a ';4 by 4'; at the lumber shop.


It will be about 3.5'; x 3.5'; by 12'





2 x 4, will be about 1.5 by 3.5 inches


ask for a ';2 by 4';





2 x 6, will be about 1.5 by 5.5 inches


ask for a ';2 by 6';





6 inches wide and 1 1/2 inch thick.


you can get a 2x6 which will be 5.5 by 1.5';








In you actually need the dimensions you state, you will have to buy a larger size and get it cut down with a special order, which is expensive. For example, you can buy a 6x6, actually 5.5 x 5.5, and get it cut down to 4x4.














You seem to have very little experience in construction. I think I knew what a 2x4 was when I was 12 years old. I hope that this bridge is not going to carry human traffic? If so, you need to get this checked by a structural engineer, or you could be liable for a lawsuit or a jail sentence when it collapses.











http://en.wikipedia.org/wiki/Timber