Yes you can use a carriage bolt
There is an inside corner piece on the Aluminum Dock frame that would make it difficult to mount the pipe sleeves on the inside. It would also be very difficult to adjust the height of the dock mounted in this manner. If you have any additional questions or we can provide further assistance please contact us at 1-888-PLAYSTAR (752-9782).
Playstar, I like your products, but you need to edit your specification for your pipe sleeves; there is no such thing as pipe given by OD; 1-7/8" pipe doesn't exist. 1.5" nominal pipe has an OD of 1.9", which is rounded up from 1-7/8" (1.875, or 1.9"). Please just say "designed to be used with schedule 40 1.5" pipe".
No the hole is only1.25 inches
Yes, although there is no plate on the oppposite side of the eood box header. You simply buy some square shouldereed 5/16" bolts and washers.
Not sure where they got 7". This thing mounts to a standard 5" backing plate perfectly.
The pipe sleeve in question uses a three and one half inch center to center bolt pattern reguiring four 3/8" galvanized carriage bolts.
No 1-1/4" with sleeve and 1-1/2" pipe without sleeve