Joe,
The 600 through 620 T&S machine have metal gears. The change over is supposed to have been with the 626. Some of the 626's have been found to have metal gears and some have been found to have nylon gears.
The 700 series did not originally come with metal gears.
I have always been under the impression that all of the T&S series could chain stitch with the proper bobbin cover plate, thread guide and feed dog plate.
Cathy
Last edited by Mizkaki; 04-03-2013 at 07:32 PM.