The small extension spring in the upper thread tension assembly of a domestic sewing machine. It sets how firmly the thread is gripped between the discs, which makes it the part responsible for whether the stitch looks right on both sides of the fabric.
Thread tension is a force, not a position. A spring within tolerance is what keeps the stitch consistent across the seam.
At this size, machine coiling rather than hand work is what keeps the force identical from spring to spring.
Older sewing machines are still in daily use and their parts are long out of production. A sample is enough to reproduce the spring.
Replace the spring rather than stretching the old one to restore tension. A stretched spring has taken a permanent set and its force will fall away again quickly.
Loose loops on the underside of the stitch caused by a tired tension spring
Obsolete sewing machine parts with no remaining source of supply
Dimensional and load figures are set per order against your drawing or sample, so they are marked TBC rather than filled with catalogue numbers.
| Product Type | Tension Springs |
|---|---|
| Raw Material Options | Stainless steel, Spring steel, Carbon steel, 65Mn, Music wire |
| Wire Diameter Range | 0.1-8 mm |
| Surface Treatment Options | Zinc plating, Nickel plating, Silver plating, Gold plating, Tin plating, Galvanizing in various colours, Dacromet, Black oxide, Phosphating |
| Standard | ISO, non-standard and OEM drawings |
| Processing Route | Material sourcing → Coiling and forming → Heat treatment → Surface treatment → Quality inspection → Packing → Shipping |
| Inspection Equipment | Grinding and shot peening machinery; Precision tensile strength testers; Magnetic powder flaw detectors |
| Packing | Plastic bags, cartons or pallets, or packing to your own specification |
| Payment Terms | L/C, T/T, D/A, D/P, Western Union, 30% deposit before production, 70% balance before shipment |
| Lead Time | 7-15 days after the order is confirmed |
| Minimum Order Quantity | Quoted per part — tell us your requirement (TBC) |
| Dimensions and Load Rating | Made to your drawing or sample (TBC per part) |
Every batch follows the same seven step route, with tensile testing and magnetic powder flaw detection carried out before packing.
Available in Stainless steel, Spring steel, Carbon steel, 65Mn, Music wire, in wire from 0.1-8 mm, with any of our nine surface finishing routes. Geometry, end treatment and finish are all specified per order.
ISO 9001, SGS certificate and RoHS report (stated on the legacy site, certificates pending re-confirmation). Certificate copies are sent on request once re-confirmed.
Against a generic small extension spring of similar dimensions, the difference is the force tolerance. Dimensionally close is not good enough for a thread tension assembly.
Yes. Send the original spring, including a broken one, and we will reproduce the geometry.
A great deal. Thread tension is sensitive, so the acceptable force band should be stated and we will test against it.
Tell us the quantity you need and we will quote it honestly rather than pushing you to a production minimum.
Send your drawing, dimensions or a sample. We will confirm the specification and come back with a price and a lead time.
