Sewing Machines
Single Needle Direct Drive Fully Automatic Stepper Motor Drop Feed Lockstitch Industrial Sewing
Model SW 8000 A
Drop feedLockstitchServo
Stitch construction · Apparel · Denim · 7 min read
Lockstitch vs chainstitch.
Two stitch families. Both common, both production-grade, neither is universally 'better.' The choice comes down to whether you need elasticity, whether the seam needs to come apart later, and whether speed beats security.
Lockstitch uses two threads — one from above (the needle), one from below (the bobbin). The needle drives down through the fabric, the bobbin hook catches the upper thread and wraps the lower thread around it, forming a knot at the meeting point in the middle of the fabric. Pull on either thread; the knot holds.
Chainstitch uses one or more threads from above, looping back into itself underneath. The needle drives down, the looper grabs the loop, and on the next stitch, the needle catches that loop and pulls it through the fabric. Each stitch links to the previous one — a chain.
The mechanical difference shows up everywhere. Lockstitch can be cut anywhere along the seam and the rest holds. Chainstitch can be unzipped from one end like a knit fabric — pull the end thread, the whole seam comes apart in seconds.
At a glance
| Lockstitch | Chainstitch | |
|---|---|---|
| Threads | Two — needle thread and bobbin thread | One or more, all from above, looping into itself |
| Elasticity | None — the locked knot doesn't stretch | Elastic — the chain stretches with the fabric |
| Removability | Cut anywhere and the rest holds | Unzips from one end — pull the tail and it comes apart |
| Speed | Slower at the same SPM (bobbin-hook sync adds cycle time) | Faster — simpler looper sync scales SPM higher |
| Typical use | Apparel construction, upholstery, leather, technical textiles | Knit hems, denim inseams, bag closing, button attachment |
Anything that has to stay sewn forever. Apparel construction (shirts, blouses, suits, dresses), upholstery seams, leather goods, technical textiles, anywhere the seam line is part of the structural integrity.
Lockstitch is the default on every industrial machine described as a "sewing machine" without further qualification. The SW 8000 A direct-drive auto lockstitch, the SW-1510L walking foot, the SW-820 post-bed double needle, the SW-845 split-bar double needle for denim outseams — all lockstitch. When in doubt, lockstitch is the safe choice.
Two limitations: lockstitch is slowerthan chainstitch at the same SPM (the bobbin hook synchronization adds cycle time), and it has zero elasticity. The locked knot doesn't stretch. On a t-shirt hem, lockstitch cracks through wash cycles. On a jean inseam, lockstitch can survive — but it's working against the fabric, not with it.
Stretch fabric / knit hems
Coverstitch (a multi-needle chainstitch variant) is the only construction that survives a t-shirt bottom hem through 50 wash cycles without cracking. The chain stretches with the fabric; lockstitch won't.
Denim and workwear inseams
Jean inseams are traditionally sewn with chainstitch on feed-of-arm machines (SW35800DNU). The denim shrinks and expands through wash; chainstitch elasticity means the seam flexes with it instead of breaking.
High-volume parallel-row work
4-needle chainstitch (SP2000-4) on jean waistbands — four parallel rows in one pass, faster than any 4-pass lockstitch alternative. The looper synchronization is simpler than bobbin-hook sync, so SPM scales higher.
Bag closing and removable seams
Industrial bag closers use single-thread chainstitch specifically because the chain is meant to come apart — pull the end thread, the bag opens. Same for tearable plastic packaging seams. Lockstitch in these applications would defeat the purpose.
Button attachment
Chainstitch button machines (SW 373 D) attach buttons with a double-knot tying cycle. The chainstitch under the button is elastic enough to absorb daily pull without snapping; the double-knot prevents the chain from unraveling at the button.
Three questions get you to the right answer:
- Does the fabric stretch? Knits, denim, performance jersey — yes. Chainstitch family (coverstitch, multi-needle chainstitch).
- Is the seam meant to come apart later? Bag closures, removable bindings, basting — yes. Single-thread chainstitch.
- Default to lockstitch. If neither of the above is true, lockstitch is right. Apparel construction, upholstery, leather goods, technical textiles. The SW 8000 A or SW-1510L family is what you spec.
Speedway machines covering both
Lockstitch and chainstitch across the catalog.
- Single Needle Direct Drive Fully Automatic Stepper Motor Drop Feed Lockstitch Industrial Sewing
- Single Needle Heavy Duty Unison Feed Walking Foot
Sewing Machines
Single Needle Heavy Duty Unison Feed Walking Foot
Model SW-1510L/DA/VS
Walking footLockstitchServo
- 4 Needle Chainstitch
Sewing Machines
4 Needle Chainstitch
Model SP2000-4
ChainstitchServoMulti
- 3 Needle Feed-off-the-Arm Chainstitch For Jeans with Differential
Sewing Machines
3 Needle Feed-off-the-Arm Chainstitch For Jeans with Differential
Model SW35800DNU
Needle feedChainstitchServo
- Chainstitch Button
Sewing Machines
Chainstitch Button
Model SW 373 D
ChainstitchServo
Common questions
- What's the mechanical difference between lockstitch and chainstitch?
- Lockstitch uses two threads — a needle thread from above and a bobbin thread from below — that knot together in the middle of the fabric, so pulling either thread holds the knot. Chainstitch uses one or more threads from above that loop back into themselves underneath, with each stitch linking to the previous one in a chain.
- Why does chainstitch unravel and lockstitch doesn't?
- Lockstitch can be cut anywhere along the seam and the rest holds. Chainstitch can be unzipped from one end — pull the end thread and the whole seam comes apart in seconds. That removability is why bag closers use single-thread chainstitch, and why lockstitch is the choice anywhere the seam has to stay sewn forever.
- Which stitch should I run for denim and stretch apparel?
- Run chainstitch. Denim inseams are traditionally sewn with chainstitch on feed-of-arm machines because the seam flexes as the fabric shrinks and expands through wash, and coverstitch — a multi-needle chainstitch variant — survives a t-shirt hem through wash cycles without cracking. Lockstitch has zero elasticity, so its locked knot doesn't stretch with the fabric.
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