Home Sewing Machine Thread vs. Leatherworking Thread

Recently, I bought a home sewing machine to use for some fabric projects and for several other reasons, which I’ll go into in a future post.  People regularly ask about using home sewing machines on leather, so it’s an area I can cover more if there’s interest. In my leatherworking studio, I have several industrial sewing machines meant for leather, and I wanted a lighter machine for sewing fabric. It was a bit of an adjustment going from industrial to home machines. Some of our readers have had the opposite experience: they start making clothes and small accessories, and later transition to making bags and other leather goods. 

I had to get a different kind of thread since most of my sewing machine work is in leather. Even the thinnest thread I had— MBT size 20—was still too thick for this home machine. Shopping for fabric thread was different than finding thread for sewing leather. For leather, your choices are polyester, nylon, linen, and polycotton. There’s a wide range of thicknesses, and you need a pretty beefy machine to handle any of them.

In contrast, thread for home sewing machines offered a wider range of compositions, like cotton and silk. The sizing was also much thinner than what I typically use for leatherworking. This intrigued me because in my collaboration with Hajime Niwa for our online course, The Zippered Wallet, he mentioned using very thin thread for wallet interiors. It was another reason to explore home sewing machines since I could put thinner thread in a home machine and not have to re-adjust my leather sewing machines. 

Home Sewing Machine Thread Sizes

When I started looking for home sewing thread, I encountered unfamiliar sizing specs; in some cases, there was no sizing information at all. The label just said  ‘cotton, 100 yards.’ Exploring more, I learned that home sewing machine thread uses a ticket number system to indicate thickness. I wrote about this system in an earlier post on thread sizes for leather.

Thread sizes using a ticket number system are, bafflingly, the least informative and yet the most common. Most home sewing machine thread is labeled with a ticket number. You’ll see thread labeled as’ 60 wt. cotton’ or ‘40 wt. polyester’.

A ticket number is just a manufacturer’s reference number, and a ticket 50 cotton can differ from a ticket 50 polyester. Ticket numbers originated from the Japanese thread measuring standard, Gunze count. There is a company, founded in 1896 (by the same name) that is still in operation today in Japan. This is a fixed-weight-based system; the number indicates the length of thread in kilometers that weighs one kilogram. For threads sized by ticket number, the number increases as the thickness decreases.

For threads sized by ticket number, the number increases as the thickness decreases.

A Gunze count number was traditionally formatted with the weight followed by a slash. Example: 50/3 Polyester. The three after the slash denotes how many plies were used to compose the thread. This system was adopted in the US and, of course, lost some things in translation. When you buy thread from a hobby or sewing supply store, you’ll typically see thread labeled as simply ‘50 wt,’ dropping the ply count. Three-ply was historically the most common composition for cotton and polyester. Some places will call out when it is not, for example, ‘50 wt. 2-ply polyester.’

Coming from using thread for leatherworking, seeing 50 wt. polyester thread was like seeing filament to me. It was so thin by comparison. The underpowered feeling of my home sewing machine made much more sense. My industrial sewing machine would barely notice this gossamer film of a thread. It seemed like this thread would break before it even got through the tension disks. 

The numbering, though, felt very familiar. The thinnest size of our MBT thread was number 20, so seeing home sewing machine thread in sizes like 30, 40, and 50 made sense. On vintage home sewing machines, they list size 20 as the thickest they can handle. If your home machine can use a size 18 or thicker, it should be able to use MBT size 20 thread. 

Size 20 thread should work for most projects that can be sewn with a home sewing machine. Some machines, like a vintage Singer 128, Pfaff 232, or modern heavy-duty machines, can take a size 20 thread. If the machine can take a size 18 needle, it should handle size 20 MBT thread. If your machine doesn’t handle these thread and needle sizes, try a 30 wt. thread in polyester. 

Sewing Machine Thread for Leatherworkers

Starting from another direction, many leatherworkers who use sewing machines start with a #69 bonded nylon. I usually steer them towards a #20 MBT too, since it is a 77 TEX, only slightly thicker than their #69 nylon, which is 70 TEX. Our studio machines include a Juki 1541 and a Pfaff 335. Both can handle size 20 with ease. They can also handle our thicker size 8. Heavier machines than what I have can use a size #5 thread. Size 5 is a 168 TEX, which is a bit thicker than #138 bonded nylon. Usually, hand-sewing leathercrafters working with 7 SPI / 3.8mm irons would use a size 5 thread, while finer work at 9 SPI / 3mm spacing uses a size 8.  More heavy-duty would be an MBT size 1, a 253 TEX thread, slightly thinner than a # 277 nylon (270 TEX).

As I do finer and finer work, I’m starting to gravitate towards even thinner threads. Size 8 MBT / Linen size 632, with 3mm spaced stitching, has been my go-to for a long time. This usually required an adjustment on the sewing machine if I got below 1mm thick leather. For example, sewing card pockets on a wallet always necessitated a test piece to get the tension right, especially if it was sewing other thicker components beforehand.

I’m looking forward to being able to bring out the home machine, which is already set for thinner work, rather than having to tune and re-tune my industrial to go between the thin and thick components. 

Learn more about sewing thread for leather in our Fine Leatherworking Thread Guide, A free series of articles about sewing thread and how to pick the right one for your leather project.