We recommend that your dock should be built with 4x6 lumber on the perimeter of your dock. Your stringers and crossmembers generally can be 2x6 lumber. However, if you are fastening 2 floats onto one stringer, you may want to consider a 4x6 at that attachment point as well, as a 2x6 just doesn't give much extra room.
These plans are designed to be decked with 2x6 treated decking lumber. If you are using alternative decking options, you will probably have to adjust the number of stringers on your frame. TREX decking must have stringers 12" apart. ThruFlow can go 15"-18" between stringers, depending on which size ThruFlow you are using.
If you have any questions, LET US HELP YOU! That's what we are here for! Also, remember that your lumber thickness will dictate which length of carriage bolts you order. Count carefully!