I don't equate tough and rare. This is a tough thread, not a rare thread.
The last five that I acquired were
Sid Smith (actually Syd)
Woodie Thornton
Frank Shaughnessy
Carlos Smith
George Paige
Interestingly the first one I acquired was Helm, who in my opinion is seen much less frequently than some of the others. Therefore order of acquisition may well be totally meaningless.
