What Durometer is my Mount?

One of the main questions we have from customers who visit us online is about the durometer of the mount they are looking to purchase.  The durometer of a mount is a rating system that tells how stiff the rubber is inside the vibration isolator.  The durometer rating is typically given by an IRH (International Rubber Hardness) scale.  Our mounts range from 35 degree IRH up to 75 degree IRH.  The lower the IRH rating of the mount, the softer the rubber component of the mount will be and vice versa.  The durometer rating will be tacked on to the end of the part number.  For example, a 17/1600-65 is a 17/1600 series Metalastik Cushyfloat that has a 65 degree IRH durometer rating.


Just about all of the mounts that we carry at Mission Sales and Supply have different variations of durometer ratings available.  Dimensionally, the mount will be the same.  The metal components will all have the same lengths, widths, and heights.  The difference in the mount will exist only in the hardness rating (durometer) of the rubber.

So how do I know the durometer of my existing mount?

Trelleborg mounts, which include Metalastik and Novibra mounts, have a couple of different ways that the durometer can be determined on the mount.

Many of the Metalastik and Novibra mounts will have the two digit durometer rating stamped into the metal baseplate of the mount.

Cushyfloat DurometerNovibra Durometer

You will see on the pictures above that the ratings are stamped into the metal baseplates of the mount.  The picture on the left is a 17/1609-75 Metalastik Cushyfloat.  These mounts will typically always have the IRH stamped near one of the mounting holes of the mount.  The picture on the right is a RA1800B Novibra mount.  Novibra mounts are slightly different in how they designate the durometer rating.  The last letter of a Novibra part will typically be a letter "A" or a letter "B".  An "A" designates a 40 degree IRH durometer rating.  A "B" designates a 60 degree IRH durometer rating.

Many of the Metalastik mounts will also use color codings to designate a durometer IRH rating.

Metalastik Durometers

Paint swatches are used to color code many of these vibration mounts.  The color coded paint swatches follow these rules:

  • Yellow - 35 degree IRH
  • Blue - 45 degree IRH
  • Pink - 50 degree IRH
  • Green - 55 degree IRH
  • White - 60 degree IRH
  • Purple - 65 degree IRH
  • Orange - 70 degree IRH

What if the color swatch or stamp is not legible?

If you are replacing an old worn out vibration mount, you might not be able to read the stamp, or the color swatch may have worn off.  In this case, we may have to work backwords to figure out which durometer rating you have.  Locate the make and model of the unit that you are isolating.  Many times, we will be able to find the specifications for your unit and be able to recommend which durometer to choose.  If you don't have that information or if product specifications are unaccessible, we may ask you to estimate the weight of your unit.  Once we know the weight of the unit you are isolating and the number of mounts you are isolating with, we will be able to accurately determine which durometer rating will give you the highest degree of isolation.

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