Hi Jean-Woo, (cc'd to list)

You will want something ideally with a 0.5" - 0.515" round hole in it
to hold the feet on the jumpseat.  My seat had a small plastic cap on one
of the feet (OD~0.5") but it was missing from the other.  I'll build it
up with tape or  something. Anyway, I suggest 3 possible fasteners for the
job:

5/8" cap screw (uses a 1/2" hex key drive)
M14 cap screw (uses 12mm hex key drive, then you'd drill it out)
M16 cap screw (uses 14mm hex key drive)

One other thing to consider is the accuracy with which you locate
these holes.  If you might not do a perfect job of locating them,
go with the 5/8" or M16.  If necessary you could even drill them out
a bit so the chair fits easily.

Some washers might be required beneath the head of the cap screws to
get the top of the cap screw at the right level for the seat.

Suggested procedure:  Drill through wooden floor with drill the
OD of the fastener head.  Drill through metal floor with drill
the OD of the fastener body/threads.  Put on some paint so your
hole doesn't rust.  Bolt it up.

Exact locations of the holes to follow, hopefully this weekend
if I can find the time.

tabe johnson/87 westy