[CR]NR Rear Der. stamped "Patent" meaning??

(Example: Production Builders)

From: <Bikerdaver@aol.com>
Date: Mon, 12 Mar 2001 21:05:22 EST
To: classicrendezvous@bikelist.org
Subject: [CR]NR Rear Der. stamped "Patent" meaning??

CR List members,
      I figured that I ought to broaden my inquiry to get a good answer from one of the experts out there. What does it mean when the NR rear der. just says "patent" with no year stamp? Cheers, Dave Anderson