Locking a stitch means securing the thread at the beginning and end of a seam so it doesn’t unravel. The most common method on a sewing machine is backstitching: sewing a few stitches in reverse over the start or end of your seam. By hand, you have several options ranging from simple knots to invisible techniques used by quilters and embroiderers. Here’s how each method works and when to use it.
Backstitching on a Sewing Machine
Every sewing machine has a reverse lever or button. To lock your stitches, sew forward three or four stitches at the start of your seam, then press and hold the reverse lever to stitch backward over those same stitches. Release the lever and continue sewing forward normally. When you reach the end of the seam, repeat the process: reverse over the last three or four stitches, then sew forward again to finish.
This creates a small overlap where the stitches double up on themselves. The overlapping threads grip each other tightly enough that the seam won’t pull apart when you trim the thread tails. Biomechanical testing has shown that backstitching provides essentially the same holding strength as tying a knot, so you don’t need to do both. Three to four stitches of overlap is plenty for most fabrics.
How a Lockstitch Differs From a Backstitch
If your machine has a dedicated “lock stitch” button (common on computerized models), it works differently from backstitching. Instead of reversing, the machine sews several tiny stitches in place, interlocking the top and bobbin threads right at that spot. The result is a nearly invisible knot buried in the fabric rather than a visible line of doubled-up stitches.
A standard sewing machine already forms what’s technically called a lockstitch on every single stitch it makes. The needle pushes the top thread down through the fabric, and a hook underneath catches it and loops it around the bobbin thread. Those two threads interlock in the middle of the fabric, which is why a properly formed machine stitch holds from both sides. The “lock stitch” button simply takes that interlocking action and concentrates it in one spot to tie things off.
Locking a Stitch by Hand
When sewing by hand, the simplest lock is a small knot at the end of your stitching line. Push your needle through to the back of the fabric, then slide it under the last stitch to create a small loop. Pass the needle through that loop and pull tight. Repeat once more for a double knot, and you have a secure anchor.
For a backstitch lock by hand, the technique mirrors what happens on a machine. After completing your last stitch, push the needle backward into the previous stitch hole so the thread overlaps. Do this two or three times, and the overlapping threads create enough friction to hold. This works well for seams that will bear weight or stress, like a shoulder seam on a bag.
The Loop Start for Embroidery
Embroiderers often avoid knots entirely because they create bumps on the front of the fabric or show through from behind. One of the cleanest methods is the loop start, which works whenever you’re stitching with an even number of strands.
Cut a single strand of embroidery floss twice as long as you’d normally use. Fold it in half and thread both cut ends through the needle, leaving the folded loop at the tail end. Push the needle down through the fabric from the front, leaving the loop on top. Bring the needle back up a short distance away (where your first stitch will land), then pass the needle through the waiting loop and pull snug. The loop cinches flat against the back of the fabric, anchoring the thread with no knot and no bulk. It’s practically invisible from the front, and it leaves the back clean enough for pieces where both sides will show.
To finish, weave the needle under several completed stitches on the back of the fabric, then trim the tail close. This locks the end without adding any thickness.
Burying Thread Tails in Quilting
Quilters face a unique challenge because their work has three layers: a top, a middle batting layer, and a backing. The standard technique is to bring both the top and bobbin threads to the same side of the quilt, tie them in a double knot a thread’s width away from the surface, then use a needle to pull that knot down through the top layer and into the batting. The knot disappears between the layers, completely hidden.
After burying the knot, slide the needle along inside the batting for an inch or so before bringing it back out, then trim the thread flush with the surface. The tail retracts into the batting and stays put. One important detail: if you’re quilting with dark thread near light fabric, keep the buried tails underneath the darker fabric so they don’t shadow through. Burying tails under a seam allowance, where the fabric is doubled, adds extra concealment.
Why Locked Stitches Come Undone
If your machine stitches keep pulling out despite backstitching, the problem is usually tension or threading, not your locking technique. When the upper and lower threads don’t interlock snugly in the middle of the fabric, individual stitches slide loose under even light pulling. A few things to check:
- Threading path. Rethread the machine from scratch, making sure the thread seats properly in every guide and tension disc. A thread that skips one guide can throw off the entire stitch.
- Bobbin seating. Confirm the bobbin is inserted in the correct orientation and that its thread passes through the bobbin case tension slot. An incorrectly loaded bobbin is one of the most common causes of stitches that pull right out.
- Tension balance. For a standard straight stitch, the threads should meet in the middle of the fabric. If you see loops of bobbin thread on top, or loops of top thread on the bottom, adjust the tension dial until both sides look even.
- Stitch length. Very long stitches (4mm or more) are inherently easier to pull out. For seams that need to hold, a stitch length between 2mm and 3mm gives a good balance of strength and flexibility.
- Lint buildup. Thread fibers and fabric dust accumulate between the tension discs over time. If tension adjustments don’t seem to make a difference, clean the discs by running a folded piece of cloth between them or using compressed air.
Pulling or pushing the fabric as it feeds through the machine also distorts stitch formation. Let the feed dogs do the work, guiding the fabric gently without forcing it forward or holding it back.
Choosing the Right Method
For everyday garment sewing on a machine, backstitching at the start and end of each seam is all you need. It takes two seconds and holds just as well as a knot. If you’re topstitching or working on something decorative where you don’t want visible reverse stitches, use your machine’s lock stitch function or pull the threads to the back and tie them off by hand.
For hand embroidery, the loop start and weaving method keeps both sides of the fabric clean. For quilting, burying knots in the batting gives the most polished result. And for any hand-sewn seam that needs to bear weight, a double backstitch at each end provides reliable holding power without bulk.