My bolts. Two from Axis & two from Bunnings hardware.
The T nuts from Axis. As you can see, the left one is how far the bolt goes through the nuts when tightened.
Yes. .50 mm side wall thickness at the narrow part. No screw threads showing through.
I occasionally spray with white lithium grease which explains the white part of the bolts that the nuts don't touch.
They'll last much longer than the three years I've had them.
I have another set that attaches my Neil pryde surf foil that I'll check. But quite sure they go all the way through the nuts as well. Had them for 6 years.