Class 15 vs 15j vs class 66 Bobbins: Which One Should You Pick?

Though bobbins are tiny in size but crucial parts of sewing. The varieties of bobbins are numerous in the market, which is easy to confuse you. Class 15, class 15J, and class 66 are 3 different kinds of bobbins.

So, you may be wondering about the differences between Class 15, Class 15J vs Class 66. 

Class 15 comes with a flat top and bottom while 15J has a slightly curved top and bottom. On the other hand, the bottom and top are curved for class 66 bobbins. 15J is only available in plastic with a blue tint body while 15 and 66 come in metal and plastic bodies with no tint.  

This was just a quick attempt. There are many more differences between them. So hang tight with the article to get a clear vision. 

Class 15 Vs 15j Vs Class 66 Bobbins: An Quick Overview

There are various types of bobbins in different shapes and styles. Class 15, Class 15J, and Class 66 are 3 different types of popular bobbins. The functionality of these bobbins is almost the same.

Though they look similar, there are some factors where these 3 kinds of bobbins lock horns. In this section, we’ll have a sneak peek at those different factors to find out how they are different from each other.    

FactorClass 15Class 15JClass 66
ShapeFlat top and bottomSlightly curved top and bottomCurved top and bottom
Compatibility Horizontal bobbin case Drop in bobbin system Vertical bobbin case 
MaterialPlastic, MetalOnly PlasticPlastic, Metal
Physical Appearance(Plastic bobbins)Transparent with no color tintTransparent with a slight blue tintTransparent with no color tint
Thread capacity Higher Less Higher 
Interchangeability NoNoNo
Price (per 12 counts)$13 to $15$8 to $10$5 to $7

It was just a quick attempt to enlighten you about the differentiating factors of class 15, class 15J, and class 66 bobbins. 

Class 15 Vs 15j Vs Class 66 Bobbins: Detailed Comparison

Now it’s time to have an in-depth discussion of those factors. A detailed comparison of Class 15, Class 15J, and Class 66 bobbins is important because it helps to ensure that you are using the correct type of bobbin for your sewing machine. 

Using the wrong type of bobbin can cause problems with stitch quality, thread tension, and even damage to the machine. So, let’s jump onto that. 

Factor 1: Height

The first differentiating factor is the height of the bobbins of class 15, class 15j, and class 66. The Class 15 bobbin is the tallest, with a height of 12mm, followed by the Class 15J bobbin, which is slightly shorter at 11mm. The Class 66 bobbin is the smallest of the three, which comes with a height of only 10mm. 

This means that the Class 15 bobbin is the largest and the Class 66 bobbin is the smallest in terms of height, while the Class 15J bobbin falls in between.

Factor 2: Diameter

While comparing Class 15, Class 15J, and Class 66 bobbins according to their diameter, it can be said that the Class 15 bobbin has a diameter of 21mm. And that is the same as that of the Class 66 bobbin.

On the other hand, the Class 15J bobbin has a slightly smaller diameter of 20mm compared to the other two types of bobbins.

bobbins diameter

Factor 3: Shape 

The shapes of Class 15, 15J, and Class 66 are completely different. The Class 15 bobbin has a flat top and bottom while the Class 15J bobbin has a slightly curved top and bottom. 

On the other hand, the Class 66 bobbin comes with a curved top and bottom. These differences in shape can affect how the bobbin fits and functions within the machine. So, understanding bobbins is a must for every passionate sewist.

Factor 4: Compatibility 

Usually, the flat top and bottom of the class 15 bobbin make it a good pick for horizontal bobbin cases. This is a universal bobbin that is used widely in almost every household sewing machine. 

Singer, Atlas, Brother, Domestic (rotary), Elna, Kenmore (rotary), Morse, Necchi, New Home (rotary/old style), Pfaff, Sewmore, Universal, White (rotary), and Wizard machines, every band’s favorite is the class 15 bobbin.


Then, the slightly curved top and bottom of the Class 15J bobbin are designed to work with machines that have a drop-in bobbin system. Singer 7400 series, Futura (CE-100, CE200), and the high-end dual voltage sewing machines from Janome are known for using 15J bobbins.

Moreover, the curved top and bottom of the Class 66 bobbin are made for machines with a vertical bobbin case. Singer models 66 series and some of the models from Baby Lock, Brother, and Simplicity use this bobbin.

So, you need to pick perfectly according to your machine and bobbin case. Using the wrong type of bobbin can cause damage to the machine and affect the quality of your stitching. Hence, always consult the manual for the correct pick.

Factor 5: Material

Material is an important factor to look at while looking for a bobbin. The construction materials of class 15, class 15J, and class 66 vary. Class 15 bobbins are constructed with plastic and metal, while Class 15J bobbins are entirely made of plastic. 

However, Class 66 bobbins are made of both plastic and metal just like Class 15 bobbins. Just like choosing between 60wt vs 90wt bobbin thread, choosing the right material is very crucial for your precious sewing machine. 

Factor 6: Physical Appearance (Plastic Bobbins)

Class 15 bobbins are transparent and have no color tint or blur, meaning they are entirely clear and easy to see through. On the other hand, Class 15J bobbins are also transparent but have a slight blue hue. Some people find this blue tint hard to see the thread on the bobbins. 

Lastly, the Class 66 bobbin is transparent with no color tint which is similar to the Class 15 bobbin. Overall, while all three types of bobbins are transparent, there are subtle differences in the appearance of each. 

The Class 15 and Class 66 bobbins are similar in that they are entirely clear, but the Class 15J bobbin has a slight blueish tint that can help reduce glare.  

Factor 7: Interchangeability

Class 15, Class 15J, and Class 66 bobbins are not interchangeable with each other when it comes to interchangeability. The Class 15 bobbin is not interchangeable with Class 15J or Class 66 bobbins, and the same is true for Class 15J and Class 66 bobbins. 

Though class 15 and class 15J may look similar in size and shape, they are not interchangeable. Choosing the wrong one can create problems like having the upper thread caught on the shuttle hook.


Factor 8: Threading Capacity 

The threading capacity also differs from each other of these bobbins. The Class 15 bobbin has a higher threading capacity than the Class 15J bobbin. Then, the Class 66 bobbin has a higher thread capacity than Class 15J bobbins.

Factor 9: Price Range

Considering the price, Class 15 bobbins are the most expensive ones, costing about $13 to $15 per pack of 12. For the same amount of Class 15J bobbins, you need to spend around $8 to $10.

Among the three, Class 66 bobbins are the cheapest. A set of 12 bobbins will cost you almost  $5 to $7.

So, Class 15 Vs 15j Vs Class 66 Bobbins: Which One to Pick?

The answer to this question is really subjective. It is difficult to provide a straightforward answer as to which bobbin is better among Class 15, Class 15J, and Class 66. Because the decision largely depends on the sewing machine you’re currently using.

Three of the bobbin consist of different shapes, sizes, compatibility, and threading capacity. And the suitability of each bobbin depends on the particular machine. So, it’s difficult to declare a clear winner.   

However, if your sewing machine requires the horizontal bobbin case, you should go for Class 15. Then, pick class 15J if your machine comes with a drop-in bobbin system. People are using vertical bobbin cases, class 15J would be the perfect choice for them.  

Also, there’s a factor of choosing metal or plastic bobbin since classes 15 and 66 feature both. So, always choose the one that came by default with your machine from the factory. Also, consult the manual for any confusion.

Furthermore, threading capacity is also an important issue to consider when choosing one. If you need to perform heavy work, class 15 and class 66 will perform best for you than class 15J.  

Frequently Asked Questions (FAQs):

What machines use Class 66 bobbins?

Class 66 bobbins are typically used for models of Baby Lock, Brother, and Simplicity sewing machines. It’s not compatible with certain machines like Bernina, Elna, Husqvarna/Viking, Janome/New Home, and Pfaff. However, it’s advisable to check your sewing machine manual or the manufacturer’s website to ensure the recommended bobbins type.

Is the SA156 bobbin the same as Class 15?

Yes, the SA156 bobbin is the same as the class 15 bobbin. However, these bobbins may be labeled as “Brother SA Bobbins” instead. It’s important to note that these bobbins are suitable for use with the Brother ST371HD sewing machine.

Does Singer 4423 use Class 15 bobbins?

Yes, the Singer Heavy Duty 4423 sewing machine requires the use of Singer Transparent Class 15 bobbins exclusively. You need to ensure that you use the correct tools for your project, including the recommended type of bobbins that came with your machine. Using the wrong type of bobbin can cause issues.  


I hope this article has sorted out all the differentiating factors of class 15 vs class 15J vs class 66. 

You’ll be able to pick the correct bobbin for your sewing machine. You need to focus on your needs first to get the required bobbin. All of them have smooth surfaces of these bobbins reduce friction, lowering the likelihood of jams occurring. 

Happy Sewing!

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