Al-Ko Trailer Tongue failure

Not so good, better would be a "reverse fishmouth" on a steel bushing that fit INSIDE the inner tube and aligned with the bolt hole. Then, properly torque the bolt (depends on grade, diameter and length) so the bolt loads a "solid structure".
Currently, the design allows for some "crush" of the tongue thus losing some of the clamping force. Threads in shear are also not a good thing for strength, but may be fine for "torque limiting" as in a snowblower auger.

Note: you could also use a length of bar stock inside the inner tube rather than my first thought.

Another note, I was describing a fix for the round tube tongue, square tube would be similar. Another thought, whatever "internal spacer" you get should have a larger diameter/size than the area under the nut or bolt head, NOT a thin tube.

While this is a thread I've done in an automotive forum, it gives some good basic engineering/hardware info......

http://www.newtiburon.com/forums/new...g-engines.html

Basically, it's about the plastic/elastic deformation of the grade/size hardware you're using and why a torque value is "approximate" based on many outside influences.