Sewing Bobbins Guide For Beginners - All About Bobbins


Sewing Bobbin basics

A bobbin is a small spool that is used in a lockstitch sewing machine to hold the lower thread. The bobbin mounts inside a bobbin-case. Sergers, Overlock machines and Chainstitch machines do not use a bobbin. All home sewing machines are lockstitch machines and use a bobbin. To read about the function of a bobbin in more detail go to the chapter "Basic Tips For Choosing A Sewing Machine".

When troubleshooting a sewing machine it is easy to overlook the simple bobbin. What could possibly go wrong with a bobbin?! Actually bobbins can cause some of the nastiest tension problems. The bobbin must turn freely or you will have tension problems, erratic stitching or thread breakage.

Unfortunately there are quite a few bobbins that are defective from the factory, these bobbins are warped or have imperfections that interfere with the bobbin turning smoothly in the bobbin-case. There are many suppliers that sell cheap bobbins of bad quality. If you get bad quality bobbins then return them to the seller, don’t try to use them, it is not worth it.

Do all bobbins fit all sewing machines?

Make sure you are using the correct bobbin for your machine, the wrong bobbin will not turn smoothly. Metal bobbins have been made for over a hundred years. There are many types that look similar but have slightly different dimensions. If you buy used equipment or have old sewing supplies hanging around then pay close attention that you have the correct bobbin for your machine and that some different type did not find its way into your bobbin drawer.

How do I know what size bobbin I need? 

Class 15 bobbin 

Class 15 bobbins are used in over 75% of all home sewing machines in use today. Class 15 bobbins come in two types as follows:

•Class 15 or industrial type A 

This is the original type with flat sides that is used in all machines with HA-1 style side-loading vertical bobbin-cases. These bobbins come in metal or plastic. The original Singer number is Class 15 and the same thing from an industrial supplier is called type A. If you buy quantities of prewound bobbins the sellers will call them type A bobbins. Do not use original flat sided class 15 bobbins in top loading machines. You may get away with it for a while, but you will eventually jam the machine.

•Class 15J or SA156

This type comes only in plastic. The Singer number is 15J and the Brother number is SA156, they are the same thing. This type has slightly curved sides (on the top and bottom) and slightly rounded edges. You can easily see the curvature if you hold the bobbin on a flat surface. This type is designed for machines with top-loading bobbin-cases. 

The slight curvature and rounding of the edges is so that as the thread passes over the bobbin (as it does in a top loading machine) it does not catch on the bobbin. Prewound type A disposable bobbins seem to work well in most top loading machines, but you should test them in your machine first before buying a large quantity to make sure they work properly. You should also ask the supplier. Class 15J or SA156 bobbins can be used in older machines as a substitute for the original class 15 bobbins with no problems.

Class 66

Class 66 bobbins are used in many Singer models made between 1930 and 1990, but are used in very few new models. Class 66 bobbins hold about 25% less thread then Class 15 bobbins. They come in both metal and plastic. All class 66 bobbins have curved sides.

Sewing Bobbins Guide For Beginners - All About Bobbins

Other home bobbin types

Some of the premium brands like Pfaff and Bernina make machines that use brand specific (non-standard) bobbins that can only be used in their machines. Most home long arm quilting machines use the larger industrial "M" style bobbins. Some heavy-duty straight stitch home machines and some premium home machines use industrial "L" style bobbins. Some home sewers use type L industrial prewound bobbins in home sewing machines that normally use Class 15 bobbins and report no problems, I have not personally tried this. The reason why they do this is that some prewound bobbin suppliers do not carry Class 15 or industrial type A bobbins.

What is the difference between L or M bobbin?

Most industrial bobbin types have letter names, A, L and M are popular types. There are many types, you can get a full listing on-line from any of the industrial bobbin suppliers, several sites have technical specifications and dimensions posted. Each type has different dimensions, use the correct type for your machine because they are not interchangeable. Watch for poor quality, it is a problem with industrial bobbins as well as home bobbins.

Sewing Bobbins Guide For Beginners - All About Bobbins

The most common industrial bobbin types are L and M. The L bobbins are smaller and are used in many drop feed machines for sewing light and medium weight fabric. The M bobbins are much larger and are used in medium and heavy duty machines of all types including most heavy duty walking foot and compound feed machines.

Testing a bobbin in the machine

This test will make sure that the bobbin can turn freely in the machine when the bobbin thread is pulled.

1.Make sure the bobbin has some thread but is not over filled. Make sure that the center end of the thread is cut off so there is no center tail of thread sticking out of the bobbin.

2.Insert the bobbin correctly into the machine and thread the machine so that the bobbin thread is coming out of the hole in the needle plate.

3.Grab the thread coming out of the hole in the needle plate and slowly pull out about a foot or two of thread.

  • Does the thread pull out smoothly but with some tension? If so then continue.
  • If you can see the bobbin on your machine, does it turn freely? If the bobbin turns freely and the thread pulls smoothly with constant tension then your bobbin is probably OK.

 5.If the bobbin does not turn freely or the thread does not pull smoothly you may have a defective bobbin. Try another bobbin.

6.Make sure the bobbin is not over filled.

7.Still not free and smooth? Usually changing to a good bobbin will fix the problem, but it could be something else.

How to inspect bobbins?

The following is a checklist of bobbin inspection items and issues to watch for, after the checklist is a picture showing some of the common problems. Replace any bobbins you find that have issues or defects.

Existing thread

Never wind thread onto a bobbin that already has thread on it. If there is thread already on a bobbin and you need to use a different color or thread type then use a different bobbin or remove the existing thread from the bobbin before you wind new thread. The reason is that the end of the existing thread may get tangled in the new thread and jam your bobbin or cause other problems and also the new thread will not wind evenly over the old thread and therefore will not unwind evenly during use and will cause tension problems.

Center tail

After you wind a bobbin you must cut off the end of the thread that is coming out from the center of the bobbin. This must be cut off close to the bobbin so that there is no tail of thread sticking out. A thread tail can interfere with bobbin rotation and cause tension problems.

Over filled 

Make sure your bobbins are not over filled with thread, 


To test for warpage, put the bobbin on your machines bobbin winder and run the machine at a low speed. As you watch the bobbin spinning around, it should not tilt from side to side. The sides of the bobbin should be centered and not move orbitally. Most bobbins are warped a tiny bit, but when you see a warped one you will know it. Test a bunch of them at a one time so that you learn what a warped one looks like.

Sharp edges or imperfections

This will make the bobbin stick in the bobbin-case and cause erratic stitching and tension problems. Feel the bobbin with your fingers to find imperfections. Feel the bobbin as it is spinning on the bobbin winder when you are checking for warped bobbins. Do a visual inspection by looking at your bobbins closely.

Dimensions out of specification 

Some bobbins are not manufactured correctly and have some part of them that is too big or too small. In all cases you can compare the bobbin you suspect to another bobbin or measure the bobbin with a micrometer.
  • Bobbin too tall - This can make the bobbin stick or can prevent the thread from unwinding and cause tension problems.
  • Outer (flange) diameter too big or too small - Too big will cause the bobbin to stick in the bobbin-case. Too small will cause the bobbin to rattle in the bobbin-case and make noise.
  • Hole diameter too small - If the hole diameter is too small the bobbin will not mount on the bobbin winder.

Metal bobbins coming apart

Some metal bobbins are made in three sections and then crimped together like a can of tuna fish. Sometimes the crimps are not tight so the sections can rotate or move separately. To test for this just grab the top and bottom of the bobbin and twist in opposite directions. If the sections are loose you will be able to rotate the top or bottom. Nothing should move separately or rotate and the bobbin should feel like one solid unit.

Plastic bobbins cracking or warping

Plastic bobbins will occasionally crack, particularly if they are old because old plastic becomes brittle. Plastic bobbins can crack and split apart when they are wound very tightly. Look for cracks when you inspect your plastic bobbins before winding or using them. If you see cracks then discard the bobbin and get a new one.


It is a good idea to periodically inspect (like before winding) all bobbins to make sure that they are OK.

Plastic vs metal

Some machines use bobbins that come in either metal or plastic. Metal bobbins tend to be a little stronger and last longer, but there is not a big difference if both are of good quality. More important than plastic vs metal is getting a good quality bobbin. A good quality plastic bobbin is much better than a poor quality metal bobbin and vice versa.

Plastic bobbins can crack and split apart when they are wound very tightly.

Metal bobbins can rust or become bent. Sometimes you can scrape the rust off with a small screwdriver and wipe any remaining rust off with a rag, if the rust is bad the bobbin should be discarded. If you spin the bobbin on the shaft of a small screw driver you can tell if it is bent. If you have a bent bobbin it should be discarded.

Proper bobbin winding

Incorrect bobbin winding causes a lot of the more nasty tension issues and it only takes a few minutes to learn to wind bobbins properly and avoid these frustrating tension problems.

Empty bobbin

Only wind thread onto an empty bobbin. Winding thread onto a bobbin that already has thread on it will cause uneven packing of the thread and can cause tension problems and jammed bobbin thread.

Bobbin winding tension

Bobbins should be wound with the correct amount of tension.
  • Too much tension during winding can cause warping or breakage of the bobbin and will cause the thread to unwind erratically during sewing causing stitch problems.
  • Too little tension during winding can cause the bobbin to have an unbalanced wind and shifting of sections of the wind (the thread on the bobbin). This can cause stitch problems while sewing.

Checking bobbin winding tension

Thread the machine as you normally would for bobbin winding. Pass the thread through the hole in the bobbin as you would to start winding, but do not run the machine, instead pull the thread and feel the winding tension on the thread. Now load another bobbin into the bobbin-case of the machine and draw the thread up through the hole in the needle plate (as you would for normal sewing). Pull the thread from the needle hole and compare that tension to the winding tension. The winding tension should be about the same as the bobbin tension of the machine.

Even winding

Watch the bobbin as it is winding make sure that the thread is evenly winding (usually from side to side). If the thread is not evenly winding then adjust the thread guides to fix the problem.

Correct filling

Do not over fill the bobbin. Over filling will cause severe tension issues or thread breakage. The thread on a wound bobbin should be at least 2mm below the rims of the bobbin at its highest point.

Sewing Bobbins Guide For Beginners - All About Bobbins

Prewound bobbins

Most prewound bobbins use special disposable bobbins that are made of a biodegradable paper material or thin plastic. This is one of the reasons that prewound bobbins are able to have about 15% to 25% more thread on them then standard bobbins. Because you discard them after use, you do not have to worry so much about bobbin problems and bobbin inspections. Prewound bobbins are available in most types (Class 15, Class 66, and most industrial types) and are available with many types of thread.

Prewound bobbins from large on-line suppliers and industrial suppliers are inexpensive if purchased in bulk. Prewound bobbins cost more than winding the bobbins yourself, but have some advantages that offset the added expense. If you are sewing a lot the total cost of using prewound bobbins may be lower once you factor in your time and all of the issues. The advantages of prewound bobbins from a high quality supplier are as follows:
  • Precision wind - Prewound bobbins are wound on expensive and high precision winding machines. These machines wind the bobbins more evenly and at a higher tension then you can wind a bobbin on your sewing machine or small bobbin winder.
  • More thread - Because of the special machines that are used, prewound bobbins have 15 to 25 percent more thread on them than bobbins that you wind your self. This means that you can sew more between bobbin changes!

Stand alone bobbin winders

Stand alone bobbin winders are available starting with small battery powered types all the way to industrial winders capable of winding many bobbins at a time. Only get a stand alone bobbin winder if you have a good reason why the expense is needed. Unless you are sewing a lot and don’t like winding bobbins on your sewing machine the built-in winder on your machine is fine.

How do I know which bobbins to buy?

With few exceptions different bobbin types are not interchangeable because they have different dimensions. It is best to use the type of bobbin recommended by the manufacturer of the machine. Use good quality bobbins. There are a lot of inexpensive poor quality bobbins being sold, don’t buy them. The amount of money that you will save buying cheap bobbins will never cover the headaches and frustration you will have from stitching and tension problems. Many times it is a good idea to buy bobbins from the manufacturer of the machine you own, because they have an interest in seeing that you do not have problems with your machine because of a substandard small part like a bobbin. Other sellers may not care. 

If you do get some bad bobbins make sure to return them to get a refund and let the seller know they were unacceptable. Most people don’t bother, that is why so many sellers are selling bad bobbins.

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