In a message dated 11/1/2014 2:02:35 P.M. Eastern Daylight Time,
jim.felder@GMAIL.COM writes:

That is  the size of the fasteners, but does not solve the problem of the
clamping  plates that actually hold the sliding seat to the floor. This is
in regard  to the early model slide in seat on the westy (and others, I
suppose) but  not the later model bolt-in, non-sliding seat in the  GLs.

the 85 westy GL's came with everything you need to install the seat already
 there.   just unbolt the beige sheetmetal track covers and slide the  seat
in and use a few of the big panhead bolts to keep the seat from sliding
from side to side. then install the track covers between the seat and slider
and  your done.

tip: put a dab of oil on the big panhead flatheads threads before u
reinstall them. trust me on that.  keep the un-used track covers in a safe  place
in your westy otherwise they will get lost/pitched and nobody repro's
those.

hmm.. idea jim?  "westy floor track covers reproduced by felder
Industries" :)  could be a good seller