besides a masturbate of Engineering, that is?

They're 8mm Socket Head Machine Screws with a section of threads ground
off to the minor diameter, leaving about 5-6mm of thread at the tip and
about 10mm at the head end. The threads engage at both the tip and head
ends.

They're used on the front seat mounts of a Sunrise Medical Rhythm power
wheelchair with a certain seating system.

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.

*WARNING: Possible redundancy