I am familiar with the Stihl 33RS chain, now known as 33RSC, but does anyone know what the 1 stands for? I was told that the chains were spun from a bulk roll that was marked "33 RS1" and the part number on the box was 3891 000 1640. A Google search produced nothing on the part number and I could only find the RS1 referenced in a couple of owners manuals. The Stihl chain ID pdf states the 1 stands for "Triple-humped Tie Strap on PM chain", so that could not apply since this is RS chain. Any help would be greatly appreciated.