This module trains one habit before anything else: turn the part over. A lockstitch and a two-thread chainstitch are almost indistinguishable on the face of a seam and cannot be confused on the back, and the same holds across the stitch catalogue. Reading a seam from the back is the fastest way to establish what a factory is actually running, and it needs no instrument.
From there the module builds outward. Six stitch classes in ISO 4915, of which twenty-two individual types carry industrial production. Eight seam classes in ISO 4916, alongside the ASTM letter codes still used in customer tech packs — SSa-1 and LSc-2 are ASTM codes, not ISO ones, and quoting both notations settles the point in one sentence. Behind each stitch sits a machine class, a bed, a feed system and a needle, and each of those brings a defect that belongs to it.
The commercial half of the subject is treated with the same care. AMANN publish the thread consumption of every stitch type: at four stitches per centimetre and 1 mm material thickness, a lockstitch seam takes 2.62 metres of thread per metre of seam and a four-needle flatseam takes 27.18. Moving a knit hem from the first to the second multiplies the thread by ten. On classes 400 to 600, between 60 and 88 per cent of that thread sits in the looper rather than the needle, which is why the thread chosen for the looper decides the cost of an overlocked seam.
The module closes where the work happens: reading a defective seam back to a probable cause, and a ten-point sequence for the specification conversation itself. The stitch specification is a cost decision before it is a performance decision, and this module gives the reader the figures to say so in front of a buyer.
Podcast: Sew Knowledge – Logic of Industrial Seams