The Can't Be Right? (part Missing?)..... Maybe Not.

Its part 10 isn't it.
I am absolutely confident there should be a washer and nut on that thread. Nothing done up tight, but it would stop the pin loosening and causing the tank mounting to come away.

Take a look around your garage for a spare nut and washer that would do the job.

 

On the Street Triple there is no nut, the bolt (part 10) just threads into the frame, however you do seem to have a lot of exposed thread compared with mine...

 

Don't panic!.... You haven't lost anything, looks the same as my 2015 SpeedTriple 94R (and the wifes 2014 StreetTriple, and my old 2008 SprintST1050 if memory serves). The casting that side is threaded for the long bolt which holds the tube in place, casting the other side is drilled to support the tube o/d. Makes for a quick and easy way to support/remove the tank. Admittedly the bolt is longer than needed but probably a generic part used on several different models.

 

Or shorten the bolt? (fellow OCD sufferer)

 

I don’t know about you, but I wouldn’t want to shorten my rod

 

When you get to my age such things are unimportant.

 

I realise I'm a bit late to this discussion, but I personally wouldn't put a nut on the end of that thread. This is because:
The frame has not been machined to create a face for the nut to seat against so it will not seat properly.
Tightening a nut onto the frame will damage the frame's surface finish.
It will also change the loading on the threads in the frame from the design intent.

As it is, a bit of thead protrusion is not a bad thing, but shortening the bolt wouldn't do any harm as long as some protrusion is maintained.