Mickey2

Some of the old machines was made to take larger needle size than #18, the limit of most modern sewing machines. I have found Schmetz in 19, and Chinese made needles can be found in upto size #22. The Cinese needles aren't as finely polished as the regular brands, so I only use them in the difficult to find sizes. They work fine in my Singer 201 and my Elna Supermatic with thicker threads. I can't remember for sure with the old green Husqvarnas like 19, 20 and 21, I think they can too, but you have to check it.

I guess the limit for these machines is about the equivalent of top stitch thread used on jeans. I can use Gütermann top stitch thread on my 201 as well as the extra strength thread. It is mostly about getting tension right and a large enough needle. You have to fuzz a bit with the bobbin tension, do drop tests. Using needle size #18, most machines do a good job with light fabric, but layers of denser fabric can be a challenge on the upper tension (you sort of never have enough). Upping the needle size usually sort out the problem, it helps the thread going through the fabric.

I'm not good with thread weight numbers, but use a bit of the mentioned top stitch thread. I don't think the later 2000 series can take needle size above 18 (110). My Bernina has a too small hole in the throat plate to use larger than 18. I think my Bernina might be able to handle top stitch thread if I bought needles with extra lage eye and the bobbin case with gold tension spring, but so far I haven't experimented or spent money on it. As mentioned, it is mostly with layers of slightly heavier fabric you get into trouble.