Thread Revisited The base tension on these old sewing machines is supposed to be set up with #50 cotton thread, as I mentioned in a previous post about tension, but I could not find any in my area. Well I finally found some. Unfortunately it was in a big spool that I can not use on my machines. However it did give me a chance to compare it to the Coats & Clark Dual Duty XL that I get at Walmart. The #50 mercerized cotton thread is quite a bit heavier than the Dual Duty XL cotton/polyester stuff. Probably the Dual Duty XL is about the equalent of #60 thread, maybe even a bit finer, which most likely explains why it matches the 11 and 12 needles so well. Therefore using the Dual Duty XL, #12 sharp needle, and medium weight fabric as I did looks to be about the closest setup I have available for setting up the tensions (Note: I am writing here about the initial setup, not the adjustments for particular fabric, thread, and needle).