AI Tech Pack Stitch Specifications: SPI, Thread Type, and Stitch Class
How to specify stitching in your AI tech pack — stitches per inch, thread types, stitch class (ISO standards), and area-specific stitch requirements.
Why stitch specs matter
Stitch specifications determine garment durability, appearance, and quality. Too few stitches per inch and seams are weak. Too many and the fabric puckers. Wrong thread type and seams break or discolor in wash. An AI tech pack with proper stitch specs ensures consistent quality from sample through production.
Skema3D generates stitch specifications based on your garment type and fabric. The AI knows that knit fabrics need different stitch types and densities than woven fabrics, and that high-stress areas need different treatment than decorative areas.
Stitch class reference
Stitch classes are defined by ISO 4915 and are the universal language for stitch specifications.
Common stitch classes for garment tech packs
| Stitch Class | Name | Threads | Common Use |
|---|---|---|---|
| 301 | Lockstitch | 2 (needle + bobbin) | Topstitching, woven seaming |
| 304 | Zigzag lockstitch | 2 | Stretch seams, buttonholes, bartacks |
| 401 | Single chainstitch | 2 (needle + looper) | Waistband, hemming |
| 406 | 2-needle coverstitch | 3 (2 needle + 1 looper) | Knit hems, sleeve hems |
| 504 | 3-thread overlock | 3 | Edge finishing, knit seaming |
| 516 | 5-thread safety stitch | 5 | Seaming with integrated edge finish |
Stitches per inch by garment area
Different areas of a garment require different stitch densities.
- Structural seams (side, shoulder, armhole): 10-12 SPI for woven, 8-10 SPI for knit
- Topstitching: 8-10 SPI — visible stitching that adds design detail
- Hemming: 8-10 SPI for single-needle, 7-9 SPI for coverstitch
- Bartacks: 15-21 stitches per bartack — reinforcement at stress points
- Buttonholes: 12-15 SPI — tight stitching for clean buttonhole edges
- Edge finishing (overlock): 12-14 SPI — prevents fraying
Thread specifications in AI tech packs
Your AI tech pack should specify thread type and weight for each application. Core-spun polyester is the standard for most seaming (strong, colorfast). Cotton thread is used for topstitching on denim (traditional look). Woolly nylon is used for overlock seaming on stretch fabrics (elasticity). Thread tex size (Tex 27, 40, 60, 80) determines thread thickness — higher numbers are thicker.
Skema3D's AI tech pack specifies appropriate thread types based on your garment and fabric. Generate your stitch-detailed tech pack at /ai-tech-pack-generator.