John Husvar fired this volley in news:jhusvar-
:

I can see *how* they work. They engages threads on both sides of a
square tube. What I can't see is: Why do it that way, considering it
only prevents the seat frame rising up off the mount? Seems like any
old
bolt would do. Or if one were a *really* anal Engineer*, a shoulder
bolt.

There are a couple of good reasons to do it that way:

1) if the "pin" is under any significant strain, a threaded body will
create stress risers that may cause it to fatique in the stressed area

2) if the item bearing on that smooth section is banging around any, it
will bung up the threads, making it difficult to remove the fastener in
the future. (A tube bushing around the bolt would help prevent that, but
is probably more cost and work to implement than the turned-down bolt
body).

LLoyd