The code has been cracked!
Thanks Matt. I was kind of hoping you would save the day.
That certainly clears things up. Now I can determine what the various rivet shank lengths are supposed to be. Then I can match them up to the Hobie part number on the Hobie rivet guide, and ultimately use the correct rivet for the job.
Many thanks.
I have a feeling that Newbies for many moons to come will be accessing and printing this post!
Dave