14/01/2026
📌DONT USE METAL BOBBINS IN A DROP IN MACHINE📌 ’its a common temptation, especially if you have a stash of old metal bobbins lying around, but using them in a modern top-loading (drop-in) machine can lead to some expensive repairs.
​Here is why you should stick to the plastic ones recommended for your machine:
​1. Magnetic Interference
​Most top-loading machines use a magnetic bobbin case to help keep the bobbin in place and maintain consistent tension.
​The Problem: Metal bobbins can interfere with this magnetic field.
​The Result: This disrupts the timing of the hook system, leading to skipped stitches, uneven tension, or "bird-nesting" (tangled thread under the fabric).
​2. Weight and Momentum
​Plastic bobbins are significantly lighter than metal ones.
​The Problem: A top-loading machine is calibrated for the low inertia of a plastic bobbin. When you stop sewing, a heavy metal bobbin has enough momentum to keep spinning for a split second.
​The Result: This extra rotation creates slack in your thread, which often causes the thread to jump out of the tension disc or jam the machine the moment you start your next stitch.
​3. Wear and Tear (The "Soft vs. Hard" Rule)
​The bobbin case in a top-loading machine is usually made of plastic or a soft composite.
​The Problem: Metal is harder than plastic. As the metal bobbin spins thousands of times, it acts like a tiny saw, scratching and gouging the inside of the bobbin case.
​The Result: Those tiny nicks and scratches will eventually snag your thread, causing it to snap constantly. Replacing a bobbin case is much more expensive than buying a pack of plastic bobbins.
​Important: Not all plastic bobbins are the same!
​Even if you stay with plastic, ensure you are using the correct Class for your machine (most common are Class 15 or L-Style). Using a bobbin that is even 1mm too tall can prevent the needle from clearing the bobbin correctly, potentially breaking your needle or damaging the hook.
​Pro Tip: If you aren't sure which one you need, check your manual or bring an original bobbin to the store to compare the height and the "flatness" of the top and bottom.