In building an elevated deck over 6x6x6 posts, a beam made of 3 pressure treated 2x8x16' (where the beams are attached to each other with FastenMaster ThruLoks) is too narrow (~5" versus 6" expected) for the galvanized-steel beam holder resting atop the post. I suppose this is due to nominal widths of the lumber, but I read this technique was acceptable if you could not get a beam and wanted to build it yourself with 2x8x16' pressure treated lumber. Where did I go wrong and what can I do to keep doing this right?
Getting the right size bracket isn't a problem, if you go to Simpson Strong Tie web site, or other comparable brand, you'll find a part number to fit your beam and post sizes. Look at the PCZ6. Or on this catalog page, the CC4.62-5.50:
Just make sure that the built up beam you made is adequately sized for the load. A built up beam made from three 2x8's may be strong enough for your deck but it is not as strong as a 6x8 beam.
If the beam of three 2x8s is sufficient for the load, consider filling out the space in the post connectors with sliced scraps of the 2x8s you used for the beam.
EDIT You could center the beam and put slices on each side.