Leather Thread: What It Is, Why It Matters, and Why We Use Size 346

Leather Thread: What It Is, Why It Matters, and Why We Use Size 346

When people look at a finished leather sheath, holster, or belt, their eyes usually go straight to the leather. What often gets overlooked — but plays just as important of a role — is the thread.

Thread isn’t just there to hold things together. In leatherwork, it affects durability, longevity, and even the overall look and feel of the finished piece. We wanted to take a moment to explain why thread matters, the different thread sizes commonly used in leatherwork, and why we’ve chosen to use the thread we do here at Lazy 3 Leather Co.

Why Thread Matters in Leatherwork

Unlike fabric sewing, leather work demands threads that are strong, abrasion-resistant, and smooth-running. Fabric can stretch and recover after being pierced. Leather does not. Once a stitch hole is made in leather, it’s permanent.

When Todd first started sewing leather, he would make mistakes — and when he did, he’d often just set the piece aside and start over. At the time, I remember thinking it was such a waste. Why not try to fix it?

Later on, when I started learning leathercraft from Todd myself, it all clicked. Leather is very different from fabric. Once you make a hole in leather, it’s there. It doesn’t stretch back or heal the way fabric can. Every stitch hole is permanent.

That was a real eye-opener for me, and it completely changed how I understood leatherwork. It’s also why material choices — especially thread — matter so much. There’s very little room for error, and the thread has to be strong, smooth, and reliable from the very first stitch.

Leather Thread Sizes: What the Numbers Mean

Leather thread sizes are identified by numbers — and generally speaking, the higher the number, the thicker and stronger the thread. Different sizes are used for different types of projects.

Here’s a general overview of common thread sizes and what they’re typically used for:

  • Size 46 – A lighter thread often used for thin leather, small accessories, or lighter-duty projects.
  • Size 69 – Common for medium-weight leather goods like bags, belts, and light holsters.
  • Sizes  92 & 138 – Heavier thread used for thicker leather and items that need more durability.
  • Sizes 207 & 277 – Strong, heavy threads often found on rugged gear, straps, and heavy leather goods.
  • Size 346 – A very heavy-duty thread where the stitching becomes both a structural and visual feature.

As thread size increases, it requires appropriate machines, needles, and setup — but it also brings added strength and presence to the finished piece.

Types of Thread Used in Leatherwork

There are several types of thread commonly used in leatherwork, each with its own strengths:

  • Bonded Nylon Thread – Nylon thread coated with a bonding agent that reduces fraying, improves abrasion resistance, and increases overall strength.
  • Waxed Thread (linen or synthetic) – Often used for hand stitching; the wax helps it glide through leather and resist moisture.
  • Polyester Thread – Known for color stability and UV resistance, often used for outdoor applications.

Each type has its place, but for thick, rugged goods that see regular use, bonded nylon thread consistently performs well.

Why We Use Size 346 Bonded Nylon Thread

Here at Lazy 3 Leather Co., we use size 346 bonded nylon thread — and we’ve been using this same thread size since Todd started making leather goods back in 2012.

At first, we were drawn to it because we liked the way it looked. Over time, as we gained experience and put our gear through real-world use, we came to appreciate the added benefits that come with this heavier thread.

Size 346 bonded nylon thread gives us:

  • A thicker, stronger stitch than what’s commonly used
  • Excellent resistance to abrasion and everyday wear
  • Long-term durability for gear that’s meant to be used, not babied

Stitching as Both Function and Design

Beyond strength, we also love how this thread looks. Because of its size and color definition, the stitching doesn’t disappear into the leather. Once a sheath is sewn, the stitches become part of the design — framing the piece and adding to its overall character.

This isn’t accidental. We choose thread that complements the leather and makes the construction visible, not hidden.

Over the years, we’ve received a lot of feedback from customers about our stitching. Many have commented that it looks solid and that the finished piece feels durable in hand. Hearing that customers notice and appreciate that detail reinforces why we’ve stuck with this thread choice all these years.

How Thread Choice Affects the Finished Piece

Thread size and type influence more than just strength. They affect:

  • How well seams handle stress over time
  • How visible and defined the stitching appears
  • How confident the piece feels during everyday use

Choosing the right thread is about balancing performance and appearance — making sure the finished piece not only lasts, but looks right doing it.

Final Thoughts

Thread might seem like a small detail, but in leatherwork it’s foundational. From durability to design, it plays a role in every stitch and every seam.

For us, size 346 bonded nylon thread has proven itself time and again. It’s strong, long-lasting, visually intentional, and well-suited to the kind of leather goods we build. It’s one of those behind-the-scenes choices that helps ensure the gear we make today is still being used and appreciated years down the road.

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