Hardness & specification
Rubber Hardness Guide: What Shore A Means
Shore A is a hardness scale commonly used for rubber and elastomers. It describes resistance to indentation under a defined test procedure. It helps specify a material, but does not by itself tell you how a finished pad or mount will perform.
Use this guide to understand the reading, record a tolerance and prepare the testing details needed for a useful quotation.
Send your hardness requirement1. Read the number together with the scale
A Shore A durometer uses a specified indenter and spring force. The scale runs from 0 to 100: a higher reading indicates greater resistance to indentation under comparable test conditions.
Write the scale as well as the value. “65 Shore A” is clearer than “hardness 65.” Shore A, Shore D and IRHD use different test arrangements; do not treat their numbers as interchangeable.
| Notation | Meaning | What still needs agreement |
|---|---|---|
| 65 Shore A | A specified hardness value on the Shore A scale. | Allowed tolerance, test method, specimen and reporting conditions. |
| 65 ± 5 Shore A | A target of 65 with a stated range of 60–70 Shore A. | How results are taken and assessed under the agreed inspection procedure. |
| Match the existing sample | A request to review a reference part. | Its material, condition, suitable measurement locations and an agreed replacement specification. |
These notation examples do not establish a default tolerance for every product. The common 65 ± 5 Shore A value on our pad selection page applies to that product reference; mount and custom-part requirements are confirmed separately.
2. Hardness is not a load-capacity rating
A higher Shore A reading does not mean proportionally higher stiffness or allowable load. For example, 80 Shore A is not a statement that a part is twice as stiff as one at 40 Shore A.
Finished-part response also depends on the compound, shape, dimensions, load direction, mounting arrangement and service conditions. Specify required load–deflection behavior or other part-performance criteria separately when needed.
For vibration pads and mounts
- Provide equipment weight, support positions and load at each point if known.
- Describe compression, shear or combined loading and installation space.
- Include operating speed or excitation frequency and the vibration concern.
- Review the required response with the geometry and material, rather than choosing hardness alone.
For other molded parts
- Describe fit, contact pressure, movement, rubbing or impact.
- State temperature and fluid or weather exposure.
- Identify critical dimensions and any rubber-to-metal bonding requirements.
- Agree relevant acceptance tests for the actual application.
The same hardness can occur in different rubber compounds. A hardness reading does not identify NR, EPDM or NBR, or prove oil resistance, wear resistance or service life. Review the rubber material selection guide alongside the hardness requirement.
3. Agree the measurement conditions
Comparable readings require a consistent procedure. Standards such as ASTM D2240 and ISO 48-4 address Shore testing; specify the applicable method and edition when required. Naming a standard here is not a claim that every product has a test report to that standard.
- Specimen: identify whether testing uses the finished part or an agreed test piece. Thickness, flatness and available surface area must suit the chosen method.
- Location: ribs, curved surfaces, thin sections and nearby metal can make a finished part unsuitable for an ordinary reading. Agree an appropriate specimen or method instead.
- Conditioning: record specimen preparation, conditioning and test temperature as required by the method.
- Reading time: agree when the reading is taken after contact, and report it consistently.
- Instrument and positioning: use a suitable checked instrument and correct positioning. Agree sampling, measurement locations and how results are reported.
A quick reading on an old or worn part is useful background, but does not automatically define a new-part acceptance limit. If the part cannot be measured appropriately, mark the hardness as “to be confirmed” and provide a drawing or sample for review.
4. Include hardness and test details in your RFQ
Copy this checklist and fill in the confirmed requirements. If no hardness has been specified, describe the application and request a review rather than selecting an arbitrary number.
Rubber hardness requirement
Part / model / drawing revision:
Material or compound code, if specified:
Hardness scale: Shore A / other specified scale
Target hardness and permitted tolerance:
Required test method and edition, if specified:
Test specimen – finished part / agreed test piece:
Measurement location and specimen dimensions:
Conditioning and test temperature:
Reading time and reporting requirements:
Application, load, movement and environment:
Required part-performance or acceptance tests:
Drawing / sample available:
Trial / production quantity:
Unknown details to be confirmed:Use the full RFQ guide for dimensions, quantities, packing and delivery details.
Open the inquiry formCommon hardness questions
Is harder rubber always better?
No. The required part response and service conditions determine the specification. Greater indentation hardness alone does not prove that a pad, mount or molded part is suitable.
Can touch or color confirm hardness?
No. Touch may help describe a sample informally, but cannot establish a specified Shore A value. Use an appropriate hardness test and an agreed procedure.
Can I convert Shore A directly into kilograms of allowable load?
No. Specify the part geometry, load direction and operating conditions, and review the relevant part-performance information or agreed tests.
What if I have only an existing sample?
Send its application, available specifications, photographs and any wear or failure observations. Confirm the replacement material, hardness and acceptance conditions before production.
Continue your selection
Mount selection → · Pad selection → · Material selection → · Prepare your RFQ →
Technical references
The ASTM D2240 overview explains the empirical nature and limits of durometer hardness. ZwickRoell’s Shore testing overview describes scales, reading time and instrument positioning. For inspection, follow the full agreed test method.
ASTM D2240: durometer hardness test overview · ZwickRoell Shore testing overview