Isacord 40wt vs Maxi-Lock 50wt for Serging
By Colibri Sewing | Sewing & Quilting Supplies | Published: 2026-10-30
Category: Comparisons
Compare Isacord 40wt and Maxi-Lock 50wt threads for serging. Learn which works best for your machine and project, with honest trade-offs.
Quick answer
For most serging on light to medium fabrics, Maxi-Lock 50wt is the better choice. If you need a bolder color for decorative serging or topstitching, Isacord 40wt works well but is heavier than typical serger thread.
Weight and thread strength
Maxi-Lock 50wt is a lighter, finer thread specifically designed for serging. Its 50wt weight and 100% polyester construction produce strong, lint-free seams that won't add bulk. Isacord 40wt is a heavier thread intended for machine embroidery and decorative stitching. While also 100% polyester, its 40wt weight is thicker, which can cause tension issues in some sergers and may create bulky seams on lightweight fabrics.
Color and visibility
Maxi-Lock in Light Grey is a soft, neutral tone that blends with light garments and knitwear, making it ideal for hidden seam finishing. Isacord in Bright Green offers a vivid, eye-catching color that stands out, perfect when you want the serged edge to be visible as a design element. If you need a subtle finish, Maxi-Lock is the way to go; if you want contrast, Isacord delivers.
Trade-offs at a glance
- Seam bulk: Maxi-Lock 50wt produces fine, flat seams that press easily. Isacord 40wt creates more noticeable bulk, especially on lightweight knits or woven fabrics.
- Tension compatibility: Maxi-Lock runs smoothly through most sergers with standard tension settings. Isacord 40wt may require tension adjustments and can cause skipped stitches on machines not designed for heavier thread. Test on a scrap before committing to a full project.
- Color range and visibility: Maxi-Lock Light Grey is ideal for invisible seam finishing. Isacord Bright Green offers a bold, decorative look that stands out on dark or neutral fabrics.
- Cost per yard: Maxi-Lock gives you 3000 yards for USD 4.40, a lower cost per yard. Isacord provides 1000 meters (1094 yards) for USD 5.27, making it more expensive per yard. For high-volume serging, Maxi-Lock is more economical.
Product facts at a glance
- Maxi-Lock Serger Thread 50wt 3000 yds – Light Grey: Maxi-Lock Serger Thread 50wt 3000 yds – Light Grey is a soft, neutral 50wt 100% polyester thread, 3000 yards per cone, designed for serging and overlocking. Its fine weight and long cone length make it a practical, cost-effective choice for everyday serging on light-colored fabrics.
Maxi-Lock Serger Thread 50wt 3000 yds – Light Grey - Isacord Thread 40wt 1000M – Bright Green: Isacord Thread 40wt 1000M – Bright Green is a vivid 40wt 100% polyester thread, 1000 meters per spool, ideal for machine embroidery and decorative stitching. The heavier weight and bright color work well for decorative serging, but the shorter spool and thicker thread may not suit high-volume seam finishing.
Isacord Thread 40wt 1000M – Bright Green
Which one should you choose?
Best for
- Serging light to medium fabrics where a flat, invisible seam is desired
- High-volume serging on a budget
Not for
- Decorative serging where you want a bold, visible thread color
- Serging on heavy fabrics or when you need a thicker thread for durability
