For this test I wanted to know the actual wall thickness of a 1" thru-hull fitting. The fitting is a standard bronze Apollo 1" thru-hull which I purchased right off the shelf at Hamilton Marine.
In this photo I am measuring the overall thickness of the thru-hull. It measured in at 2.99 millimeters thick.
I am illustrating this to show why simply sticking a valve onto a thru-hull (without flange) is not as strong or as safe as using proper flanged seacocks and threading the thru-hull into a flange or thru-hull. Simply threading a valve directly to a thru-hull, with no flange, increases the risk that the thru-hull could be snapped off.
I personally had this happen to me when a spare alternator hit my ball valve that was screwed directly to a thru-hull and cracked it. This is the number one reason I will now only use properly flanged seacocks and thread the thru-hull into it.