Check Spring (Part #43946 / 8511) – For Singer 31 & 331K
Ensure perfect tension and precise loop formation with the Check Spring (Part #43946 / 8511). This critical tension component is engineered specifically for Singer 31 and 331K industrial machines. It acts as the buffer for the upper thread, taking up the slack during the needle's descent and ensuring the thread is controlled at the exact moment the hook catches the loop.

Key Performance Features
High-Resilience Spring Steel: Manufactured from premium-grade tempered steel, providing the perfect balance of flexibility and "snap-back" required for high-speed industrial sewing.

Consistent Tension Control: Regulates thread slack to prevent "bird-nesting" and looping on the underside of the fabric.

Precision Coil Geometry: Designed to fit perfectly into the tension assembly of the Singer 31/331K series, ensuring smooth operation without binding or sticking.

Fatigue Resistant: Built to withstand millions of cycles, maintaining its tension strength even under the constant stress of heavy-duty production.

Orders are typically processed within 1–3 business days.

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We stand behind the quality of the products we sell.

• Genuine OEM parts are covered by the manufacturer's warranty where applicable.

• Aftermarket and generic parts are covered against manufacturing defects.

• If you receive a damaged, defective, or incorrect item, please contact us within 30 days of delivery.

• Warranty does not cover damage caused by improper installation, misuse, normal wear, or modifications.

If you have any questions, our support team is happy to help before or after your purchase.