The best O-ring measuring tool depends on whether you need to measure a loose seal’s dimensions, identify a standard AS568 size, or remove seals from equipment. The slide gauges below measure multiple dimensions, while the cone tools focus on identifying standard sizes. The Kit King USA set also includes a double-ended seal pick. Compare the listed measurement ranges and standards before choosing a tool.
| Product | Best For | Key Feature |
|---|---|---|
| National O-Ring Slide Gauge | Measuring several dimensions | Measures ID, OD, and thickness |
| Kit King USA Sizer Cone and Pick | Standard AS568 sizes and seal removal | Measures ID and thickness; includes pick |
| National O-Ring Slide Gauge | AS-568/BS1806 identification | Displays AS size number |
| Mr O-Ring Blue Sizing Gauge | Standard rings up to 13 inches ID | Plastic slide gauge |
| Mr O-Ring Sizing Cone | Quick AS568 identification | Dash numbers molded into steps |
National O-Ring Slide Gauge
This plastic slide gauge is designed to measure an O-ring’s inner diameter, outer diameter, and thickness. Its listed standards are AS-568 and BS1806, and a small window displays the AS size number.
Best for: Buyers who want one tool to compare several dimensions and identify a standard size. It is a practical choice when you need more than an inside-diameter measurement.
Limitation: The listed standards are AS-568 and BS1806, so verify that your seal follows one of these standards before relying on the size display.
Kit King USA Sizer Cone And Pick
This set combines a sizing cone with a double-sided hook and pick. The cone measures inner diameter and thickness and identifies 184 popular imperial AS568 sizes, covering listed inside diameters from ¼ inch to 5⅝ inches and five cross sections: .070, .103, .139, .210, and .275 inches.
Best for: Mechanics or maintenance buyers who need to size standard imperial O-rings and remove seals. The pick has a full hook and a 90-degree hook, and the listing also describes use for other seals, including piston seals and PTFE seals.
Limitation: Its stated sizing coverage is for standard imperial AS568 rings and specified cross sections; it may not identify a nonstandard seal.
National AS-568/BS1806 Slide Gauge
This slide-style plastic gauge is listed for measuring inner diameter, outer diameter, and thickness. It supports AS-568 and BS1806 sizing, with an AS size number shown in a small window near the top.
Best for: Buyers seeking a slide gauge with a visible size-number readout and measurements for three O-ring dimensions. It is a better fit than an ID-only tool when you want to compare the ring’s overall dimensions.
Limitation: It is a plastic gauge, and the product information does not provide a maximum measurable diameter. Check the tool’s scale and fit for your ring size.
Mr O-Ring Blue Sizing Gauge
This plastic slide gauge measures standard-size O-rings with an inside diameter up to 13 inches. Its straightforward slide format makes it a candidate for buyers who need to measure larger standard rings.
Best for: Anyone who wants a slide gauge with a stated maximum inside diameter of 13 inches. Choose this if that capacity matches your seals and you prefer a simple sizing tool.
Limitation: The listed features do not specify measurement of outer diameter or thickness, or identify a size-number display. Choose a multi-dimension gauge if those functions are essential.
Mr O-Ring AS568 Sizing Cone
This 17½-inch-tall plastic cone is designed for quick identification of standard AS568 O-rings. Its dash numbers are permanently molded into steps around the cone, allowing the user to match a ring to a marked step.
Best for: Buyers who mainly need to identify standard AS568 dash numbers quickly. The molded markings make it a direct alternative to a slide gauge when standard-size identification is the priority.
Limitation: The listed features do not specify a measurement range or separate inner-diameter and thickness readings. It is not the strongest choice if you need numerical measurements for nonstandard rings.
Buying Guide: How To Choose An O-Ring Measuring Tool
Do you need measurements or a size number?
Choose a slide gauge when you need to compare dimensions such as inner diameter, outer diameter, or thickness. Some slide gauges also display a standard size number. Choose a cone when quick identification of a standard AS568 dash number is the main task.
Which dimensions should the tool measure?
Inner diameter describes the opening inside the ring. Cross-section thickness describes the material’s thickness. Outer diameter measures across the outside of the ring. Check the product’s stated functions: not every tool lists all three measurements.
Does your O-ring follow a standard?
Confirm whether the seal is an AS568, BS1806, or another standard size before selecting a gauge. Standard-specific tools may not identify an unusual or custom ring. For nonstandard seals, a tool that measures dimensions directly may be more useful than one that only identifies standard numbers.
Do you also need to remove seals?
If removal is part of the job, the Kit King USA set includes a double-sided pick with two hook angles. A sizing cone or slide gauge alone is described as a measuring or identification tool, not a seal-pulling set.
How should you compare listed ranges?
Match the tool’s stated coverage to the seals you expect to measure. The Kit King USA cone lists its AS568 diameter and cross-section range, while the Mr O-Ring blue gauge lists support for standard rings up to 13 inches in inside diameter. Some listings do not provide a maximum range, so confirm suitability for unusually large or small rings.
Frequently Asked Questions
What is an O-ring sizing gauge used for?
An O-ring sizing gauge measures or identifies a seal’s size. Depending on the tool, it may measure inner diameter, outer diameter, thickness, or match the ring to a standard dash number.
Can a sizing cone measure O-ring thickness?
Some cones are listed for thickness measurement. The Kit King USA cone measures thickness and inner diameter, while the Mr O-Ring cone’s listed features emphasize AS568 identification.
What does AS568 mean on an O-ring tool?
AS568 is a standard size system referenced by several tools in this list. A compatible gauge or cone can help identify rings by standard size, subject to its stated coverage.
Should I measure a worn O-ring?
A worn or deformed ring may not represent its original dimensions accurately. Use the tool’s measurements alongside the application’s required standard or replacement specifications when available.
Do all O-ring tools measure the same dimensions?
No. Some slide gauges list inner diameter, outer diameter, and thickness; others list only standard-size measurement or identification. Review each tool’s stated functions before buying.