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# Correctly Measuring an O-Ring – How to Do It

If you have the correct tools available to use, the process of measuring an O-Ring is relatively simple. All you need to undertake the measurement process is a clean surface that is level, an O-Ring and a device that you can use to measure such as a calliper although other measuring tools can be used such as size charts, gauges and cones.

O-Ring Measurement Process

In order to correctly measure an O-ring, you need to follow the process below:

1. Put the O-Ring on a surface that is flat and is free of any debris
2. Identify the inside diameter (ID) of the O-ring as well as the outside diameter (OD).
3. Now you will need to measure the width of the O-ring or the cross-section (CS) of it. This can prove a challenge, but it can be measured by gently pressing the calliper ends onto the O-Ring.

It is possible to use just two dimensions to determine an O-Ring size; for example, the inner diameter and the cross-section measurements. If you know two of the three dimensions, then you can use the following formulas to calculate the third.

OD = ID + (2 x CS)

ID = OD – (2 x CS)

CS = (OD – ID) / 2

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