Of the four features that identify an O-ring (material, durometer, color, and size) the hardest part of an order is typically figuring out and accurately communicating the exact size required. Applying tried-and-true techniques for figuring out the right size will save you time up front, frustration, and extra money down the road. Continue reading to discover how to size an Standard O-ring supplier correctly the first time.
Measurement of O-Ring CS and ID
CS (cross-section) and ID (inner diameter) measurements are the most accurate ways to size an O-ring, offered by a Standard O-ring supplier. The ideal instrument for measuring the cross-section is a caliper, often known as a micrometer. If you don’t have one, you can get a close estimate using a variety of alternative sizing tools.
It is also recommended to use a caliper when measuring really small IDs. The best tools to use for larger IDs (above 6 inches) are an O-Sizer or a Pi-Tape.
After determining the O-ring’s CS and ID, using a AS568 O-Ring Size Chart, you may determine whether the O-ring’s CS and ID fall within one of the “standard” sizes.
O-Ring Sizes and Tolerances in Metric and Standard
Metric (mm) or standard (inch) dimensions can be used to define all O-rings. However, as AS568 is the most widely used standard in the USA, it is advisable to refer to it if the O-ring size matches that. If not, you might be able to find a “metric” O-ring that has the required dimensions.
Tolerances, is a crucial factor to consider while sizing O-rings. There will always be some variation in the dimensions of O-rings due to manufacturing limitations. These variations are known as tolerances, and the allowable standard tolerances are listed in the AS568 O-Ring Size Chart or the Metric Tolerances Chart for Metric O-Rings, both of which were previously discussed.
For instance, the cross-section of each AS568 100 Series O-ring with a tolerance of ± .003 is .103″. Consequently, the cross-section could measure as small as .100″ or as large as .106″.
Sizes of the O-Ring Standard (AS568)
You most likely have a standard-sized O-ring if the CS is one of the standard AS568 sizes, such as .070, .103, .139, .210, or .275 inches. Look up its ID on a sizing chart and measure it. You have a standard size if the ID is listed on the chart (or is within tolerance). Your O-ring size can be found by looking up the 3-digit “dash” number.
Sizes of Metric O-Rings
You might have a “metric” O-ring if the CS is not one of the standard AS568 sizes. Simply measure the CS and the ID in this case as was said previously to determine the appropriate size on a metric size chart. Metric sizes are distinguished by their CS X ID, which has the format #.##X###. A 1 mm CS X 5 mm ID O-ring, for instance, would be designated as 1.00X005.
Summary
In this blog post, you got an insider view of sizing an O-Ring right the first time. Now you can easily buy the right size O-rings from an O-rings supplier in your area, or at a reputed O-rings retail website.