Understanding Bearing Internal Clearance with Ceramic Hybrid Ball Bearings

    Have you ever looked at a bearing part number and wondered what the suffix C3 (or C2, or C4) means? Knowing what they stand for can help you get the right ceramic hybrid bearing for your specific application. Read on, and we’ll help you “decode” this important portion of a bearing part number.

    The suffixes C0 through C4 in a bearing part number refer to a bearing’s internal clearance value and have to do with what’s called “radial play”. Radial play is the radial internal clearance between the balls and races, and is the measured value of the total movement of one ring with respect to the other in a plane perpendicular to the bearing axis. Radial play can also be referred to as“internal clearance”.

    The following is a list of bearing clearance values and what they mean:

    • C0 – Referred to as “standard clearance”. Normally, there are no markings on a bearing with a C0 clearance value.
    • C2 – Refers to a “less than standard clearance”. Bearings with this type of clearance are uncommon and have very limited uses.
    • C3 – Refers to a “greater than standard clearance”. This is the most common type of bearing, and is the correct choice for the majority of applications.
    • C4 – Refers to “greater than C3 clearance”. Not as common as C3, but often specified in small engine crankshaft bearings.

    In any bearing, including ceramic hybrid ball bearings, some internal clearance is necessary to the ensure that the bearing turns freely, without binding. But note that these clearance values are very small. For example, a 25mm bearing with a “standard fit” will have an internal clearance of about a half a thousandth of an inch. The same bearing with a C3 fit will have about one thousandth of an inch clearance. This value is less than the diameter of a human hair! Internal clearances are also relative to the bearing’s bore size (the amount of radial play will increase as the bore size increases).

    The radial play for a given bore size is not an exact value, but a range. For example, a 6205 C3 bearing (25mm bore) has a radial play value that falls between .0006” and .0010”. The same bearing in a C4 clearance has a clearance range of .0011” to .0015”. In a properly assembled bearing, the clearance will generally fall in the middle of the tolerance range.

    A small amount of extra clearance is usually not a problem, but any amount of negative clearance (interference) can be a big problem, resulting in increased friction, heat, and ultimately in early fatigue failure. Therefore, it is always better to err on the side of a bearing that is a little loose, rather than one that is a little tight. It is also important to note that the radial clearance value that matters most is that when the bearing is installed and up to operating temperature.

    There are certain times when it is necessary to specify a bearing with increased clearance (C3 or C4):

    • When there is a significant press fit on the shaft and/or housing
    • When there is a very slight misalignment between the bearing housing and shaft
    • When using in elevated temperatures

    All three of the situations mentioned above will cause a bearing’s internal clearance to decrease. To compensate, it is important to install bearings with greater than standard internal clearances.

    CBR Bearing is one of the few specialty bearing companies that measures the internal clearance of each an every ceramic hybrid ball bearing we sell. They use their own custom-built test fixtures that are accurate to .00005” (‘fifty millionths of an inch). This allows them to accurately and professionally set up the proper clearance in every bearing.

    When you purchase ceramic hybrid ball bearings from CBR Bearing, you can have confidence that the products you purchase will be well made, with the proper amount of radial play. If you are ready to make a purchase, or if you have more questions about our ceramic hybrid ball bearings, contact us. We are always happy to help a customer and will make sure you get the exact bearings you need for your application.

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