Your best option is to special order through Home Depot.
3/8" lags will work fine for the installation.
They are set bolts and designed to lock the pipe into place to avoid turning as it's set into the lake bottom.
Generally if installing on a wood frame you would use hex bolts with washers and nylock nuts.
You would want at least two. One on each side keeping it stabilized.
You can utilize a Pipe Wrench, or purchase a Tommy Dock Auger Wrench which is available on Home Depot.com
There is no specific amount of years with regards to longevity of the product as different fresh water lakes have varying amounts of ph, inorganic carbon and hardness.
You can utilize a large strap wrench to avoid marking the pipe or Tommy Docks does offer a Auger Wrench for sale as well.
The ID is 1 1/4" and the OD is 1.66".