Instruments as per ISO 48
Determination of hardness (hardness between 10 IRHD and 100 IRHD)
ISO 48 specifies four methods for the determination of the hardness of vulcanized or thermoplastic rubbers on flat surfaces (standard-hardness methods) and four methods for the determination of the apparent hardness of curved surfaces. The hardness is expressed in IRHD. The standard method covers the hardness range from 10 up to 100 IRHD.
These standards are different primarily in the width of the indenting ball and the scale of the indenting strength, these being chosen to suit the particular application.