How To Choose The Best Thread For Finer Leather Work

A while back, a Reddit user asked, “[what is the] best thread for finer work?” Many people wrote in to say that our linen thread was at the top of their list.

Update: Since originally publishing this post, I’ve extensively written about sewing and thread. I recently updated this post to reflect those articles and added more insight to help you choose the best thread for finer leatherworking.

Stitching Consistency is the Most Important Thing

No matter what thread you choose, sewing consistently uniform stitches will make your work look ‘finer.’ The thread can be beautiful, but if the stitches are all over the place, that will be the first thing people notice. I did a post a while back rounding up several saddle stitching videos, and every person had an almost mechanical replication of their sewing movements. They didn’t squirm to see if their awl was going in correctly or peeking back and forth from one side to the other. Consistency of movement will transfer to your stitching.

The back side of the stitch is a gotcha for most beginners. One of my teachers described it as the ‘beginner’s mountain range’ because the haphazard stitch pattern looked like a panorama of the Alps. As you improve, your awl more consistently goes into the stitch mark perpendicular to the surface. When sewing, you can isolate both axes where rotation happens: front to back, where the stitches look smaller or larger and top to bottom, where the stitches go either closer to or further from the edge. Front-to-back rotation typically happens when you flick your wrist going into the stitch. When you do that, the awl tip follows an arc path in right-to-left motion. The top-bottom rotation usually comes from raising or lowering your elbow.

If you want to improve your stitching technique, try holding a big wooden spoon and, without thinking about it, make the same movement as you do when you use your awl. Hold the spoon part like the flat of your awl. The more extended handle will exaggerate the movement, and you’ll be able to see where you tend to drift.

A more recent technique is to omit the awl entirely and pre-punch your holes. Traditional pricking irons are named after what they do: mark the surface of the leather so you can later open the hole with an awl. Newer irons have very narrow tapers, which allow you to punch through the leather. Your traditional irons will also do this up to about ~1.8mm / 4 oz.  By punching all the way through, you eliminate one variable, your awl work, to get more consistent sewing. This method is not entirely carefree, especially with thick leather or multiple layers. With thicker material, you introduce the risk of non-parallel holes. If you inadvertently angle your irons, you can enter at one distance on the top of the leather and exit closer or farther from the edge.

Match Stitching to the Thickness of the Thread

Update: I wrote a detailed article on how to match your thread to your stitches per inch. The advice below on linen thread is similar. I’ve expanded the chart below to include linen, MBT polyester, and other common thread measurement.

The above image shows our different thread thicknesses in the same 9 SPI stitch count. 0.1mm doesn’t seem like a lot, but you can see the difference in thickness, especially side by side.

I recommend 532 or 632 thread at 9 SPI if you use just one size pricking iron and thread. The 9 SPI is an all-around good size for both bags and accessories. I use this most often, and it works great for finer work.

If you’re going to 7 SPI, I recommend the thicker 432. The smaller threads don’t look great at low stitch counts and won’t hold the seam as long. The 432 looks good for larger work like handbags and duffels. Again, you can use 9 SPI and 632 for larger work, but some styles match better with the thicker look.

Many synthetic thread users use a medium-weight thread like #5 MBT for 7 SPI. For a chunkier, 7 SPI or 6 SPI, use 332. Its thicker diameter gives weight to the stitches and works well with similarly designed work.

If you use larger than 6 SPI, I’d recommend a different thread line with thicker sizes. I don’t see the larger sizes used much in luxury/fine work, though they are often used in more rugged styles.

If you’re doing very fine work like watch straps, I’d recommend 832 at 10 or 11  SPI. This gives a more delicate feel to the work, and the thread looks more appropriate to the project size.

Recently, I tore down a luxury bag and saw that two thread thicknesses were being used on different parts. They used the equivalent of 332 for the straps and handles at 7 SPI and 632 at 9  SPI for the rest. The size difference seemed more for aesthetics since both would hold up equally well.

By the numbers, here are the thicknesses of our different threads, linen thread and MBT Polyester, for comparison:

Small Details Make Finer Work

Making finer work is all about the details. Often, many minor differences separate the very best work from its competitors. Our thread is re-twisted to make it a little bit denser than others. You would think that the difference would be minor, but as others have confirmed, it really makes the thread stand out.

Similarly, you can do several things to improve your work’s thread-related details. Below are a few that you can try individually or all together.

Contrasting stitch. Use a lighter color thread on a darker leather or vice versa to highlight your stitching work. It is also a way of challenging yourself to improve your sewing because it will stand out.

Match the color to the lining or edging. Matching the exterior thread to the bag’s interior can make the colors “pop” when the bag is opened. A good example of this technique is to use red thread on the outside of a gray bag to highlight a red interior.

The backstitch is a prominent part of the seam. The additional thread makes it stand out from the rest of the line, and people’s attention can naturally gravitate toward it. It is often in a noticeable location, like the top of a bag or right next to the hardware. If you learn to sew ambidextrously, as I teach in our case course, you can place the backstitch consistently in the right place.

Update: When I originally posted this article, people were doing terrible things with their stitch holes. I would say we’re past this today, but I still hear from people doing the below.

Minimize the hole size. If you’re using a drill or lace marker, mark your stitches with a tool that makes smaller holes, like a pricking iron or pricking wheel. Minimizing the hole structurally strengthens the stitches and gives it a nicer look.

Sew instead of riveting. Using rivets is a big time saver for creating belts or straps, but sewing them can create a finer look. Though it takes more time to sew a strap closed than riveting, the results are worth it.

What Is The Best Thread For Leather Work?

The best thread is the one that matches the needs and style of your project. If you’re sewing a simple strap to repair a little kid’s tote, you might not need to bust out the Lin Cable to make a piece to last the ages. On the other hand, is your child’s first elementary school backpack that you intend for them to give to their kids? You should pull out all the stops in making that heirloom piece. The best thread for leather is a combination of the right choice, usage, and technique.