1. I would recommend the stainless steel bolts. They cost more but are stronger and avoid the rusting and corrosion problems of steel bolts. The thing I like best - the stainless steel lag bolts have sharper well defined threads which cut nicely into a properly pre-drilled pilot hole for a superior holding power.

Carriage bolts on the other hand are a common fastener. But, due to their shape, you've to drill a hole to put it in. Thus requires a little 

Bolting deck beams to the posts sounds like a good idea, right? And it is—as long as you're not solely relying on the bolts to hold your deck together and keep it solid and sturdy for years. Bolts alone are not going to secure those beams and posts together tightly enough. And over time, the nuts and bolts you use are going to loosen.

Fortress® Evolution steel deck framing and stair system is the next evolution in decking. It's a smarter galvanized steel system designed by deck builders, for deck builders. Our total solution system features joist, beams, ledgers, brackets and accessories. The Evolution Single Beam to Post Bracket is designed to connect a beam to a 3.5-in post.

I need to correct the main girder 4x4 supports for my deck. It is 4' off the ground. The 2x8 beam girders are carriage bolted to the 4x4 support posts.

Then we use the ½" carriage bolts to firmly attach the beam to the side of the vertical member of the post. You mentioned using one of the Simpson Strong Tie 4x adjustable post cap. That is a good solution but is intended for securing a beam directly on the top of a post of identical dimensions.

It sits on the top of the support post like a cap. But its U shaped sides cradle a 3.5" wide beam usually made from two 2x pieces of lumber with a 1/2" spacer between. This is perhaps the fastest and easiest way to secure beams to 4x4 post. The load is on top of the post, not bolted sideways where all the load is held by carriage bolts. 6x6 Posts

Carriage & Through-Bolt Replacement The 6 1/4" is engineered to connect 4x4 posts to 2x joists. The 7" is engineered to connect two 2x beams to a notched 6x6 post. The 8" is engineered to connect 4x4 posts to a double rim joist or single rim joist and 2x blocking. The 9 1/2" is engineered to attach a 6x6 post to two 2x beams.

the fasteners staggered between the two rows at the spacing indicated by the IRC table. For example, on a deck with a joist span of 15 feet, the lag screws 

ThruLOK is a code-compliant through-bolt and carriage bolt replacement fastener for multi-ply beams, deck posts and carrying beams that can be attached

beam (bottom of the I-beam) in A Zones. Anchoring the home shall be according to Oregon Residential Specialty Code, Appendix E, Section AE101 and AE102. Note: Effective April 1, all home installations shall be anchored against the wind. Typical wind anchoring provisions in most cases is equivalent to typical flood