ISO 505 safety stitch (5-thread safety stitch)

The safety stitch ISO 505 belongs to stitch class 500 (overlock class) according to ISO 4915 and combines two complementary stitch formations in a single sewing pass: a 3-thread overlock stitch (class 504) neatens the cut edge, and parallel to it a second needle inside the seam allowance forms a 2-thread chainstitch (class 401), which carries the actual joining load. The result is a highly durable, clean and stretch-capable seam — the classic “jeans seam”.

The machine (typically a 5-thread overlock from Juki, Pegasus, Brother or Union Special) works with one or two needles, three to four loopers and two thread systems; the knife trims the edge cleanly directly before the stitch is formed. Safety stitches are used for jeans side seams, work trousers, workwear overalls, sportswear and wherever high tension and abrasion meet a seam that has to be stretchy yet firmly closed. Thanks to the double chainstitch, the joint is markedly stronger than a plain 4-thread overlock (ISO 514) — important for safe seating areas in trousers and for workwear according to EN 13688.

• ISO 505: 3-thread overlock (cl. 504) + 2-thread chainstitch (cl. 401)
• Thread consumption: about 20 m of thread per 1 m of seam
• Advantage: extremely strong joint plus clean edge neatening
• Standard use: jeans side seams, workwear overalls, chinos