See slide 11 within: http://www.awc.org/Publications/DCA/DCA6/DCA6.pdf
As per its details, 1/2" thick lag bolts are used. One could possibly use 3/8 thick lag bolts (and double their amount) but do keep in mind, more "little lag bolts" into a vertical 2xN stud weakens it as much as less "larger lag bolts" in the same stud. Besides that, minimim code is probably 1/2" thick in your region. And like all minimum code, there's many proven reasons behind it. With this in mind, using 1/2" thick lag bolts is probably best.... Do call your local inspector to confirm if more "smaller thickness" lag bolts can be used for your Deck. After all, he/she will be doing its final inspection (hopefully).
Also... If you don't like using lag bolts, one might be able to use 1/2" thick galvanized threaded bolts and use large washers on each side. Both inner and outer sides. This is an alternative "Ledger board" attaching method on slide 11 as well.
Hope this helps...