Which bobbin class does my machine take? Measure it, then match the manufacturer's dimensions

After reading this you will be able to identify your machine's bobbin class from the bobbin in your hand — by diameter, height, end-face shape, color tint and material, checked against published manufacturer dimensions — for the cases those figures can settle, and you will know which cases they cannot settle and what to look up instead.

Bobbin class is a physical fit specification, measured in millimeters. It is not a brand and not a product line. "Class 15" describes a disc of a particular height and diameter with particular end faces — nothing about who made it. This matters because the failure mode you are trying to avoid is not "it won't go in." It is "it goes in and sews badly."

The short answer

Do not choose by brand, and do not choose by whether a bobbin drops into the well. Choose by measurement. Take the bobbin your machine came with, measure its outside diameter and its overall height, note whether the two end faces are flat or slightly domed, hold it to the light for a color tint, note metal or plastic, and match all five against the manufacturer's published table below. If the machine came with no bobbin, skip to "If you have no bobbin at all."

Two bobbins that share a class name can still be non-substitutable. SINGER publishes the clearest example: Class 15 metal and Class 15 transparent are listed at identical dimensions — 7/16" high, 13/16" diameter — and SINGER still says on each row not to substitute one for the other. Same class name, same stated numbers, still not interchangeable. SINGER's own instruction is to "Use only bobbins that are the same class/style as those that come with your machine." (published)

Read SINGER's table in inches, not in millimeters

SINGER publishes ten bobbin styles with height, diameter, and in most cases an end-face description, a color or material note and a substitution warning. Two rows are incomplete: Touch & Sew carries no substitution warning, and Futura carries no end-face description.

SINGER's millimeter column does not convert correctly from its own inch figures, and the errors are larger than rounding. 5/16" is given as 10 mm on the Class 66 transparent row and as 8 mm on the Touch & Sew row; the true value is 7.94 mm, so the same fraction is printed two different ways and one of them is 2.06 mm out. 6/16" is given as 11 mm when it is 9.53 mm. 1-1/8" is given as 27 mm when it is 28.58 mm. 7/16" is given as 12 mm on the Class 15 rows and 11 mm on the Class 66 metal row; it is 11.11 mm, so the Class 66 row is the accurate one. (observed, and recomputed from SINGER's own inch figures)

The practical consequence: measure in inches, or convert SINGER's inch figures yourself. Do not match calipers against SINGER's millimeter column. The converted column below is this page's arithmetic on SINGER's inch figures, not a SINGER publication.

Where the bobbin goes, and what that does not tell you

Janome publishes a document titled "What Kind of Janome do I have? Presser Foot Attachment Quick Reference Guide." It is a presser-foot guide, and it opens with a question worth borrowing: "Where do you insert your bobbin?", with two answers — "Horizontal Rotary Hook Bobbin" or "Front Loading Vertical Oscillating Hook." Its other two questions are maximum stitch width and shank height. Janome asks the bobbin question to classify the machine for presser-foot selection, and says nothing there about bobbin class. (published)

It is still worth answering, because it tells you what kind of object you are looking for: a drop-in top-loading bobbin and a bobbin that seats in a removable case are different mechanisms. But be clear about the limit — no source used on this page maps hook type to a candidate list of bobbin classes, and this page will not invent one. Knowing you have a front-loading vertical oscillating hook does not narrow you to a class. What does narrow it, for one brand at least, is the part number: Janome lists its standard bobbin as part 102261103, clear plastic imprinted with the letter J, fitting "all Janome Sewing and embroidery machines except the 1600P, HD9, MB4, and MB7." One brand, one bobbin, four named exceptions. (published)

The four classes you will meet on non-SINGER machines

Sewing Parts Online states that "About 95% of household sewing machines use the following 3 bobbins" — Class 15, L-style and M-style. (published) Class 15J is included in the table below because it is the one most often confused with Class 15. Both published unit systems are given because packages and charts use different ones.

The two sources do not convert to each other, so do not read a row across as one measurement. Wawak's 13/16" is 20.64 mm against Sewing Parts Online's 20.3 mm — a 0.34 mm gap. Wawak's 7/16" is 11.11 mm against Sewing Parts Online's 11.7 mm for the same class — a 0.59 mm gap. On M-style the gap is 0.5 mm. Treat every figure here as a nominal published value, not a tolerance. (inferred, by converting Wawak's fractions and comparing them to Sewing Parts Online's millimeter figures)

L-style and Class 15: a fit relationship, not a recommendation

L-style and Class 15 share a diameter. Both published references state the consequence in the same direction: an L-style bobbin will physically enter a machine built for Class 15, and a Class 15 bobbin is too wide to enter a machine built for L-style. Wawak words it as "in a pinch, they can sometimes be used" in a Class 15 machine. (published)

Read that as a fact about geometry, not as advice. Physical entry is not correct operation. An L-style bobbin is narrower than a Class 15 by about 2.8 mm on Sewing Parts Online's figures and about 2.38 mm on Wawak's, so it holds less thread. (inferred, from the published widths) What a narrower bobbin does to tension in a case built for a wider one is not something this page can source, and the published references do not address it. This page is not telling you to substitute one for the other.

One thing that gap does settle: it is far larger than the disagreement between the sources. The two sources differ by 0.59 mm on Class 15's width, and Class 15 and L-style differ from each other by more than four times that. So height genuinely does separate those two classes, whichever source you use.

Class 15 versus 15J: what the numbers can and cannot settle

This is the question most often asked by people with an inherited machine. Sewing Parts Online gives the 15J as approximately 20.4 mm and Class 15 as approximately 20.3 mm — a 0.1 mm difference between two figures the source itself marks approximate, which is below the precision that source is claiming. SINGER's inch figures put the gap the other way and much wider: 13/16" against 3/4", which is 20.64 mm against 19.05 mm, a 1.59 mm difference. (observed, with the millimeter conversions recomputed here) The two sources are not really in conflict; one is simply not reporting at a precision that answers the question. (calculated)

Either way, calipers alone are a poor tool for this one pair. Three other things settle it. The end faces: SINGER describes Class 15 as "completely flat" and 15J as "very slightly curved," and Sewing Parts Online describes a "slightly curve to the sides" on the 15J. The color: SINGER describes Class 15 transparent as "Transparent, no color tint" and Class 15J as "Transparent with very slightly blue color tint." And the part number in your manual or on the original package. (published)

Brother's support answer illustrates why part numbers beat class names. It states the machine "uses the Brother SA156 bobbin, which are high plastic Class 15 type bobbins," adds that "if bobbins from other models are used, the machine will not operate correctly," and that "metal bobbins should not be used in this machine." Brother's own product page for SA156 prints no class designation at all — it gives "High quality clear plastic bobbins. 7/16 inch deep." That 7/16" depth matches SINGER's Class 15 height rather than SINGER's 15J height of 6/16". The part number is checkable against the manufacturer. The class name is not. (published)

Class tracks the model, not the brand

A published machine-to-bobbin chart makes this concrete. Within Bernina: the 440 and 440QE are listed Class 15, the 450 is L-style. The 163 is listed Class 15, and the 165 appears three times — plain "165" as Class 15, "165 (Artista)" and "165E (Artista Heritage)" as L-style. Within Singer: the 221 and 222 Featherweights and the 301 are listed "Unique," and the 9020 is the chart's single Class 66 row. (published)

Tallying the chart by row gives about 560 model rows: roughly 311 Class 15, 176 L-style, 64 M-style, 10 Unique and exactly 1 Class 66. Class 15 is more than half the chart; Class 66 is one machine in it. (observed, by extracting the PDF to text and counting the class label on each row; two rows carry two labels and are counted in both families)

What is reported to go wrong

The following are reported by others and attributed as such. On a reader-question thread at National Sewing Circle, the writer reports that on her machine "the class 15 bobbin wound just fine, but the 15J just spun in place" on the bobbin winder. A commenter, Diana Neill, reports owning two machines, one calling for 15 and one for 15J: "Although they both seemed to work interchangeably while I used them, I ended up having to replace my bobbin case in the one that uses 15." (observed, as reports)

Another commenter, Cindy Heinz, reports the reverse case: she took 15J bobbins from a Singer and tried them in "my Brother which was supposed to use 15. It did not work well. The 15J is shorter side to side than the 15." She adds that generic Class 15 bobbins from a general retailer work fine in the same Brother and in a Babylock. That second half agrees with Brother's own specification. (observed, as a report)

Brother's support answer puts the manufacturer's position more sharply: "use of any other bobbin may result in injuries or damage to the machine." Wawak states separately that material is not interchangeable either — "Like its size, a bobbin's material is not interchangeable." (published)

One more point argues against reusing a scavenged or dented bobbin. Sewing Parts Online states that "even the slightest nick will cause skipped stitches and thread nests." (published) One published standard shows the principle is taken seriously in manufacturing, though it does not cover your machine. Indian Standard IS 8892-1978 applies only to bobbins for "sewing machines with rotating hooks for industrial use"; clause 3 requires they be made from steel and clause 6.3 requires nickel plating. It therefore says nothing about domestic Class 15, 15J, L or M bobbins, and nothing about plastic ones at all. Within its own scope it requires that "the thread handling areas of bobbins shall be free from sharp edges and burrs" and holds outer-diameter eccentricity "within 0.2 mm of total indicator reading." (published) That a burr-free surface is a specified manufacturing requirement for industrial bobbins is a reason to take a nicked domestic bobbin seriously. It is not evidence about domestic bobbins. (calculated)

If you are chasing skipped stitches and the bobbin checks out, the needle is the next variable — see the needle guide for reading system, size and point off your own machine.

How to measure yours

1. Measure the outside diameter across the flanges. Digital calipers are ideal; a steel rule will separate a nickel-sized bobbin from a quarter-sized one but will not separate 15 from 15J.
2. Measure overall height, flange face to flange face. This is the number that reliably separates Class 15 from L-style — a gap of 2.4 to 2.8 mm depending on the source, which is several times larger than the sources disagree with each other. You can see it by eye once you know to look.
3. Look at the end faces edge-on. Completely flat, or slightly domed? SINGER's table turns on this for both the 15/15J pair and the Class 66 pair.
4. Hold the bobbin to the light. SINGER describes Class 15 transparent as "Transparent, no color tint" and Class 15J as "Transparent with very slightly blue color tint." (published) Compare against a known bobbin if you have one; a faint blue cast is hard to judge in isolation.
5. Note the material. Metal and plastic are treated as separate specifications by SINGER, Brother and Wawak alike — not as a finish choice.
6. Match against the tables above, using SINGER's inch figures or the converted millimeter column, never SINGER's own millimeter column. If two rows still fit, you need the model, not the measurement.
7. If your measurements match no row, stop. The cross-brand table covers four of what Sewing Parts Online says are "over 60 different bobbin styles available." Several others sit in the same caliper range: Class 66 at about 20.5 by 10.9 mm, the Bernina 0115367000 at about 20.5 by 10.6 mm, the Juki 270010 at about 20.8 by 8.7 mm, and the Husqvarna Viking 4125615-45 at about 20.9 by 10.4 mm. (published) The Juki case is the sharp one: at about 20.8 by 8.7 mm it is within caliper noise of L-style, and Sewing Parts Online states specifically, "You should not use L Style bobbins in place of the Juki 270010." A near miss means look up your model, not pick the closest row.

If you have no bobbin at all

Find the model number, then the manual, then the bobbin part number. SINGER's Australian site gives model number locations by era: machines since 2000 carry "the model number and serial number on the back; usually located on the left-hand side"; 1990–1999 machines have it "on the handwheel sied of the machine. Typically near the on/off switch" (the typo is the source's); 1970–1989 machines carry it "on the front left hand side of the machine"; 1960–1969 machines "on the front right hand side of the machine above or below the stitch length control"; pre-1960 machines have it "typically located on the right hand side on a small plate on the front of the machine." (published)

With the model number, pull the manual. SINGER's help article on finding a product manual directs owners to support.singer.com for "free copies of complete user's manuals, stitch guides, and machine updates"; that site carries SINGER, Husqvarna Viking, PFAFF and mySewnet. Brother, Janome and the others run equivalent libraries. The spec field you are looking for is the bobbin part number in the accessories or parts list — not the word "bobbin" in the threading diagram. A part number is checkable against a manufacturer's own page. A class name is not. (inferred, from the Brother and Janome part-number listings above)

Failing that, measure the bobbin case or the bobbin well opening rather than a bobbin, and use that to narrow the family — then confirm against the manufacturer's page before buying. Shank height and stitch width, the other two questions on Janome's presser-foot guide, belong to a different purchase; see the presser foot guide.

Check it on your own equipment

These take you to the manufacturers and standards bodies the page draws on, so you can look up your exact model.

• Manufacturer specification
  SINGER's bobbin selection guide (all ten styles with dimensions, color and warnings) (opens in a new tab)SINGER's own table of ten bobbin styles, each with height and diameter in inches, a description of the top and bottom faces, a color or material note, any model restriction, and a per-row warning about what not to substitute. Match on the inch figures; SINGER's millimeter column does not convert correctly from them. — help.singer.com
• Official support page
  Brother support: which bobbin your Brother machine uses (opens in a new tab)Brother's support answer naming the SA156 bobbin as a Class 15 type, stating that bobbins from other models will prevent correct operation, that metal bobbins must not be used, and listing the several hundred Brother model designations the answer applies to. — help.brother-usa.com
• Official support page
  SINGER support: free manuals for SINGER, Husqvarna Viking, PFAFF and mySewnet (opens in a new tab)The manufacturer's support site for those four brands, which is the destination SINGER's own help article gives for free user's manuals, stitch guides and machine updates. With your model number in hand, pull the manual and read the bobbin part number out of the accessories or parts list. — support.singer.com
• Standards reference
  IS 8892-1978, the published standard for industrial rotating-hook bobbins (opens in a new tab)The full Bureau of Indian Standards text, free, two pages. It covers steel, nickel-plated bobbins for industrial rotating-hook machines only — not domestic Class 15, 15J, L or M — and sets requirements for burr-free thread handling areas and 0.2 mm eccentricity. — law.resource.org