Manufacturer · Fashion Accessories
Leather thread thickness is chosen according to the thickness of the leather, the type of seam and the needle. For machine sewing of leather, threads from Tex 45 to Tex 135 are most commonly used, and for hand sewing waxed threads from 0.45 to 1.0 mm. The thicker the leather and the more pronounced the seam, the thicker the thread, and the needle and stitch length increase with it.
How leather thread thickness is designated
Leather threads use four different systems, and this is exactly what confuses buyers. It is important to know which one your supplier uses:
- Tex – mass in grams of 1000 m of thread. A higher number means a thicker thread. This is the most precise system and the standard for bonded threads.
- V number – an American trade designation for bonded threads, approximately equal to Tex (V69 ≈ Tex 70).
- Ticket number (Tkt) – a trade number based on the metric count. Here a higher number means a finer thread.
- Diameter in mm – used mainly for waxed threads for hand sewing.
Chart: Tex, V number, ticket and needle
The equivalents below are approximate, because they depend on the material and coating. Always check the data sheet of the specific thread.
| Tex | V number | Ticket (approx.) | Needle Nm (approx.) | Typical application |
|---|---|---|---|---|
| 30 | V30 | 80–60 | 80–100 | Gloves, fine small leather goods, clothing |
| 45 | V46 | 60–50 | 100–110 | Leather garments, linings, wallets |
| 70 | V69 | 40–30 | 110–130 | Footwear, bags, upholstery |
| 90 | V92 | 30–25 | 130–140 | Backpacks, more visible seams |
| 135 | V138 | 20 | 140–160 | Decorative seams, belts |
| 210 | V207 | 10–15 | 180–200 | Saddlery, heavy belts |
| 270 | V277 | 8–10 | 200–230 | Special heavy products |
Thickness according to leather thickness
A good seam looks proportionate to the material. Too thick a thread in thin leather looks heavy and the holes weaken the leather. Too thin a thread in thick leather sinks in and the seam gets lost. A guide by leather thickness:
| Leather thickness | Machine sewing | Hand sewing (waxed) |
|---|---|---|
| up to 1 mm | Tex 30–45 | 0.35–0.45 mm |
| 1–2 mm | Tex 45–70 | 0.45–0.65 mm |
| 2–3 mm | Tex 70–135 | 0.65–0.8 mm |
| over 3 mm | Tex 135–270 | 0.8–1.2 mm |
Needle and bobbin thread
In machine sewing of leather, the needle and bobbin threads are not always the same. Often a thread one step finer is put in the bobbin, for example Tex 70 on top and Tex 45 underneath. This fits more thread on the bobbin, and the stitch knot stays in the middle of the material. When the seam is visible on both sides – on belts, straps and bag handles – use identical threads so both sides look the same.
Thread thickness and stitch length
A thick thread requires a longer stitch. If the stitches are too dense, the holes merge and the leather tears along the seam line like perforated paper. As a guide:
- Tex 30–45: stitch of about 2.5–3 mm;
- Tex 70–90: stitch of about 3–4 mm;
- Tex 135 and heavier: stitch of about 4–6 mm.
In hand sewing the stitch length is determined by the spacing of the pricking iron. Irons with 2.7–3 mm spacing are combined with 0.4–0.5 mm thread, those with 3.85–4 mm spacing with 0.65–0.8 mm, and wider spacing with threads of about 1 mm.
How to choose the thickness for a specific product
- Define the seam's function. Is it structural (load-bearing) or decorative? Structural seams are sized by load, decorative ones by appearance.
- Measure the total thickness. Add up the thickness of all layers the needle pierces, including lining and reinforcement.
- Check the machine. Every machine has a maximum needle size and a maximum thread thickness for the bobbin.
- Do a test seam. Sew on a piece of the same leather and check the look, tension and strength.
Decorative seams: when thickness is part of the design
For decorative seams the thickness is chosen not by load but by appearance. Brands often use a thicker thread in visible places – along the edge of a belt, on bag handles, on the top edge of a shoe – and a finer one on the hidden structural seams. This makes the product look substantial and handcrafted without loading the whole construction with heavy thread. If you use two different threads, order them from one colour range and check the shade in daylight, because the thicker thread always looks slightly darker.
Common mistakes in choosing thickness
- Comparing ticket numbers from different manufacturers without checking Tex – the same number can mean a different thickness.
- Switching to a thicker thread without changing the needle – the thread rubs in the eye and breaks.
- Too short a stitch with a thick thread – the leather tears along the seam.
- Different thickness top and bottom on a seam visible from both sides.
The general logic of thread numbering is the same for textiles – you will find more about thread types in our threads category.
Advice on thickness from Polkom
Polkom is a manufacturer and wholesale supplier of sewing accessories. In our threads for footwear and leather category we offer bonded and waxed threads in various thicknesses, and for the product's brand – leather labels. Send us the leather thickness, product type and machine model via our contact page – we will recommend a specific thickness and send samples.
