What is a bar tack?

A bar tack is a short block of dense zigzag stitching that takes load at a point where a seam would otherwise tear.

Where they belong.

• The top corners of a patch pocket
• Both ends of every belt loop
• The top of a vent or a slit
• The bottom of a fly opening
• The ends of a buttonhole, where the machine puts them automatically
• The base of a pocket welt

How to sew one without a bar tack function. Set a zigzag 3 to 5 mm wide, reduce the length to 0.3 to 0.5 mm, and sew for 6 to 10 mm. Secure both ends. That is a bar tack, and it is what the automatic function does.

On computerised machines there is often a dedicated bar tack programme where you set the length once and the machine repeats it identically. Use it when you need several to match — belt loops in particular.

Practical points. Sew it through as many layers as the strain will travel through, including any facing or lining underneath. Reduce speed; dense stitching at speed heats the needle and shreds thread. And put a stabiliser behind it on anything light, or the dense block will pucker.

Thread choice matters more here than elsewhere. A bar tack is visible and it is structural, so polyester rather than cotton, and topstitch thread if it is meant to be seen.

The alternative on very heavy fabric is a small triangle or square of straight stitching, which spreads the load over a larger area.