To measure a ball bearing, use calipers to take three dimensions: the bore (the inside diameter of the inner ring), the outside diameter of the outer ring, and the width across the rings. Those three numbers identify the size. If the part number is still readable, it tells you the same information, and this guide shows how to decode it.
How do you measure a bearing with calipers?
Wipe the bearing clean so grit does not throw off the reading. Digital calipers that switch between millimeters and inches help, since you will not know which system applies until you measure.
- Bore: open the inside jaws inside the inner ring and read the widest point. Take a second reading a quarter turn around and confirm the two agree.
- Outside diameter (OD): close the outside jaws across the outer ring at its widest point.
- Width: close the outside jaws across the flat faces of the rings. On most deep groove bearings the inner and outer rings are the same width.
Bearings are made to standard dimensions, so round to the nearest standard size: 16.98 mm is a 17 mm bore and 0.499 inch is a 1/2 inch bore. An odd metric value such as 12.7 mm usually means an inch bearing, since that is exactly 1/2 inch.
How do metric bearing part numbers work?
In a number such as 6203, the first digit, 6, means single row deep groove ball bearing, the second digit gives the dimension series, and the last two digits give the bore.
- 6000 series: the lightest of the three common series, with the smallest OD and width for a given bore. Browse the 6000 series.
- 6200 series: the middle series in OD and width. Browse the 6200 series.
- 6300 series: the heaviest, with the largest OD and width for a given bore. Browse the 6300 series.
- 6700, 6800 and 6900 series: thin section bearings with a smaller OD and width for a given bore, from the thinnest 6700 series through the 6800 and 6900 series.
The last two digits work the same way in every series. Codes 00, 01, 02 and 03 stand for 10, 12, 15 and 17 mm bores. From 04 upward, multiply the code by 5: 04 is 20 mm, 05 is 25 mm, 10 is 50 mm and 22 is 110 mm.
So a 6203 has a 17 mm bore, 40 mm OD and 12 mm width, while a 6003 (17 x 35 x 10 mm) and a 6303 (17 x 47 x 14 mm) share the bore with different footprints. See the 6203 solid oil bearing.
How are small metric bearings numbered?
Bearings with bores under 10 mm use three digit numbers, and the last digit is the bore in millimeters. A 608 has an 8 mm bore, 22 mm OD and 7 mm width. A 625 has a 5 mm bore, 16 mm OD and 5 mm width. A 688 has an 8 mm bore and 16 mm OD in the thin 68x series.
These sizes, along with small inch sizes, are in our miniature and instrument bearings collection; the 608 miniature solid oil bearing is a typical example.
How do inch bearing part numbers work?
R series: in the R4 through R24 sizes, the number after the R is the bore in sixteenths of an inch. R4 is 4/16, or 1/4 inch. R8 is 1/2 inch, R16 is 1 inch and R24 is 1 1/2 inch. Smaller inch sizes use other codes, so measure them. Browse the R series or see the R8 solid oil bearing.
1600 series: these inch bearings have an extended inner race. The inner ring is wider than the outer ring and projects past it on both sides, so it can seat against a shoulder or a locknut without the outer ring rubbing. The numbers do not encode the bore; a 1616 has a 1/2 inch bore and a 1 1/8 inch OD. Record the outer ring width and the full inner ring width separately.
Browse the 1600 series or see the 1616 solid oil bearing.
What do 2RS, ZZ, 2Z, RS, Z and C3 mean?
Old bearings usually carry a suffix that describes what covered the gap between the rings:
- 2RS: two rubber seals, one on each side.
- RS: one rubber seal.
- ZZ or 2Z: two metal shields, written either way.
- Z: one metal shield.
- C3: internal clearance greater than normal, meaning more free play between the rings and balls. It is not a seal code.
A solid oil bearing is sealed with solid oil, so there is no seal or shield suffix to choose. The 6203-SL (Standard) or S6203-FGSL (Food Grade) replaces a 6203-2RS, 6203ZZ, 6203-2Z or open 6203 at the same bore, OD and width. If your old bearing was marked C3, mention it when you email us and we will confirm the fit.
How do you use the Bearing Finder?
The Bearing Finder turns your three measurements into a part number.
- Enter the bore, outside diameter and width you measured.
- The finder shows the matching size from our 204 metric and inch sizes.
- Open the product page and pick Standard or Food Grade; both share the same dimensions.
- Add to cart. Every bearing is filled to order in Glendale, California and ships in 7 to 10 business days by UPS or USPS, within the United States only.
If nothing matches, email info@solidoilbearings.com or use the contact form with your three numbers and a photo of the old markings. We reply within one business day. Our FAQ covers shipping and ordering.
Frequently asked questions
What are the dimensions of a 6203 bearing?
A 6203 bearing has a 17 mm bore, a 40 mm outside diameter and a 12 mm width. Our 6203-SL and S6203-FGSL solid oil bearings share those dimensions and replace any 6203, whatever its seal or shield suffix.
What is the difference between 2RS and ZZ?
2RS means two rubber contact seals and ZZ means two metal shields on a greased bearing. A solid oil bearing is sealed with solid oil, so the choice does not apply; one part number covers both.
Can I measure the shaft instead of the bearing?
Yes. The shaft diameter where the bearing sits matches the bore, and the housing seat matches the outside diameter. Measure the width of the seat to complete the set.